MEDICAL    *SCH<S>©L 


THE  AMERICAN  ANATOMICAL  MEMOIRS 


THE  MORPHOLOGY  AND  EVOLUTIONAL 
SIGNIFICANCE  OF  THE  PINEAL  BODY 

BEING 

PART    I 

OF 

A  CONTRIBUTION  TO  THE  STUDY  OF  THE  EPIPHYSIS 

CEREBRI  WITH  AN  INTERPRETATION  OF  THE 

MORPHOLOGICAL,  PHYSIOLOGICAL  AND 

CLINICAL  EVIDENCE 


FREP^RICK  ITILNEY,  M.D.,  PH.D. 

PROFESSOR  OF  NEUROLOGY,  COLUMBIA  UNIVERSITY 
AND 

LUTHER  F.  WARREN,  A.B.,  M.D. 

PROFESSOR  OF  MEDICINE,  LONG  ISLAND  COLLEGE  HOSPITAL 


1919 


PUBLISHED  BY 
THE  WISTAR  INSTITUTE  OF  ANATOMY  AND  BIOLOGY 

PHILADELPHIA 


(NJUO'< 


ill 


CONTENTS  OF  PART  I 

1.  Introduction 5 

2.  Nomenclature 7 

3.  General  review  of  the  literature 9 

4.  The  comparative  morphology  of  the  pineal  region 17 

1.  In  cyclostomes 21 

2.  In  selachians 23 

3.  In  ganoids ! 25 

4.  In  teleosts 27 

5.  In  dipnoi ; 29 

6.  In  amphib:a 30 

7.  In  reptilia ? 31 

8.  In  aves 36 

9.  In  mammals 37 

5.  The  comparative  embryology  of  the  epiphyseal  complex. 39 

1.  In  cyclostomes 39 

2.  In  selachians : 41 

3.  In  ganoids 48 

4.  In  telecasts 50 

5.  In  amphibia 53 

6.  In  reptilia .' 56 

7.  In  aves 67 

8.  In  mammals ' 72 

6.  The  comparative  anatomy  and  histology  of  the  epiphyseal  complex 80 

1 .  In  cyclostomes 80 

2.  In  selachians 92 

3.  In  ganoids 98 

4.  In  teleosts 103 

5.  In  amphibia 114 

6.  In  reptilia. 119 

7.  In  aves 148 

8.  In  mammals 155 

7.  Discussion 196 

1.  Significance  of  the  pineal  region 

2.  Evidence  based  on  the  gross  morphology  of  the  epiphyseal  complex. ...  203 

a.  Phyletic  constancy 203 

6.   Phyletic  variation  and  morphologic  specialization 205 

c.  Relative  constancy  of  the  epiphyseal  complex  with  reference  to 

other  structures  of  the  pineal  region 211 

d.  Relative  constancy  of  the  epiphyseal  complex  with  predomi- 

nance of  the  proximal  portion 

3 


4  .  CONTENTS 

e.   The  increase  of  the  epiphysocerebral  index  during  life  in  man..  213 
/.   The  resistance  to  the  encroachment  of  the  corpus  callosum  in 

mammals 216 

3.  Evidence  based  on  the  histology  of  the  epiphyseal  complex 217 

4.  The  relation  of  the  parietal  eye  to  the  pineal  body 226 

5.  The  phylogenetic  significance  of  the  parietal  eye  with  reference  to 

vertebrate  and  invertebrate 233 

8.  Summary  and  conclusions 238 

9.  Bibliography 240 


1.  INTRODUCTION 

"Son  siege  au  milieu  de  parties  tres-importantes  de  Pence- 
phale,  sa  Constance  chez  Thomme  et  le  vertebres,  font  pourtant 
presumer  que  ses  usages,  s'ils  ne  sont  pas  d'un  ordre  aussi  impor- 
tant qu'on  le  supposait  a  Tepoque  des  Esprits  Vitaux,  n'en  sont 
pas  moins  reels  et  tres-interessant  a  connaitre." 

Legros.     These  de  Paris,  1873,  page  24. 


"Vix  ulla  unquam  corporis  nostri  particula  tantam  famam 
inter  eruditos  non  modo,  sed  etiam  inter  illiterates  nacta  est,  ac 
cerebri  sic  dicta  glandula  pinealis."  These  words  written  by 
Soemmering359  in  1785  still  hold  true.  Not  only  did  this  organ 
attract  much  early  medical  attention,  but  its  reputation  was 
extended  by  the  metaphysicians  and  even 'further  increased  by 
the  satirical  literature  of  an  uncommonly  virile  period.  Descartes 
(1649) 89  in  his  discourse  on  the  sources  of  the  human  passions, 
expressed  the  belief  that  the  pineal  body  was  the  seat  of  the  soul. 
This  interpretation  passed  current  during  the  epoch  of  Vital 
Spirits.  It  did  not,  however,  go  altogether  unassailed.  Voltaire411 
so  successfully  made  it  the  subject  of  parody  that  his  whim- 
sical conception  of  the  pineal  body  became  more  influential  than 
the  origina  hypothesis  of  Descartes.  According  to  Voltaire, 
the  epiphysis  should  be  regarded  as  the  driver  which,  by  means  of 
two  nerve  bands,  guides  the  action  of  the  cerebral  hemispheres. 
These  nerve  bands  were  long  referred  to  by  the  anatomists  as 
"the  reins  of  the  soul/' 

During  the  past  hundred  years  an  increasing  volume  of  re- 
search has  revealed  the  difficulties  in  the  epiphyseal  problem 
and  shown  how  far  we  are  from  a  solution  of  it.  In  fact,  the 
views  advanced  by  the  students  of  this  subject  are  so  numerous 
and  often  so  divergent  that  any  decision  at  the  present  time 

5 


6  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

would  seem  ill-advised.  The  separation  between  those  who 
consider  the  pineal  body  a  useless  vestige  and  those  who  assign 
to  it  extensive  responsibilities  in  the  sphere  of  internal  secretion 
is  too  great  to  be  reconciled  on  any  but  the  most  careful  investi- 
gation of  the  grounds  for  their  differences.  The  phylogenesis  of 
the  organ  among  the  vertebrates,  especially  in  its  relation  to 
the  third  or  parietal  eye,  as  well  as  the  significance  of  the  struc- 
ture as  a  possible  mark  of  identification  in  the  line  of  evolution 
from  the  invertebrate  to  the  vertebrarte  phylum,  has  raised  many 
perplexing  questions.  Although  the  researches  of  morphologists, 
physiologists,  and  clinicians  have  established  many  significant 
facts,  it  still  remains  to  assemble  this  evidence  as  much  in  its 
entirety  as  possible  in  order  to  furnish  a  satisfactory  basis  for 
the  discussion  of  the  problem. 

It  is  the  purpose  of  this  work  to  gather  the  recorded  facts 
concerning  the  pineal  body  and  present  them  in  several  parts 
under  the  following  headings: 

Part  I.  The  morphology  and  evolutional  significance  of  the 
pineal  body. 

Part  II.  The  physiology  and  pathology  of  the  pineal  body. 

Part  III.  The  clinical  aspects  of  the  pineal  body. 


THE  MORPHOLOGY  AND  EVOLUTIONAL  SIGNIFICANCE 
OF  THE  PINEAL  BODY 

The  morphological  problem  of  the  epiphysis  may  be  for.- 
mulated  in  the  following  questions: 

1.  What  is  the  significance  of  the  pineal  region  in  its  relation 
to  the  epiphysis? 

2.  Is  the  pineal  body  a  vestige  or  is  it  an  organ  in  some  way 
necessary  to  metabolism? 

3.  Does  its  structure  furnish  evidence  of  its  function? 

4.  What  relation  does  it  bear  to  the  third  or  parietal  eye? 

5.  What  is  the  phylogenetic  significance  of  the  parietal  eye 
with  reference  to  the  vertebrates  and  invertebrates? 

Before  submitting  these  questions  to  discussion,  it  seems 
advisable  to  offer  the  evidence  as  much  in  extenso  as  is  practi- 
cable, having  particular  regard  for  historical  sequence. 

2.  NOMENCLATURE 

The  pineal  body  was  known  to  the  Greeks  and  called  by 
them  the  <ro^a  /aowtSes  and  KWVO.PLOV  because  of  its  conical 
shape.  It  was  also  termed  the  epiphysis  because  of  its  relation 
to  the  rest  of  the  brain.  Latin  authors  refer  to  it  as  the  turbo, 
corpus  turbinatum,  glandula  turbinata,  glandula  piniformis,  glan- 
dula  conoides,  conarium,  penis  cerebri,  and  virga  cerebri. 

Because  of  its  resemblance  to  a  pine  cone,  it  was  called  by 
Chaussier63  and  Willis429  the  corpus  pineale.  It  has  been  called 
by  the  Germans  the  Zirbel  and  Zirbeldruse,  a  designation  which 
doubtless  has  led  to  the  more  or  less  general  use  at  present  of 
the  term  pineal  gland.  Several  of  the  early  writers  called  it  the 
glandula  superior  in  contradistinction  to  the  pituitary  gland 
which  was  referred  to  as  the  glandula  inferior. 

Since  all  of  these  terms  were,  in  the  main,  devised  to  meet  the 
conditions  in  man  and  the  higher  mammals,  it  might  be  expected 

7 


8  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

that  they  would  not  prove  wholly  satisfactory  for  some  of  the 
lower  vertebrates.  Earlier  works  on  the  pineal  body,  even 
such  as  dealt  with  ichthyopsid  and  sauropsid  forms,  employed 
the  terms  epiphysis  and  corpus  pineale  with  so  little  discrimina- 
tion that  these  definitions  became  rather  vague.  The  com- 
plexity of  the  structure  in  the  lower  reptiles,  in  amphibia,  and  in 
fish  is  such  that  it  may  only  in  a  very  general  way  be  denomi- 
nated the  epiphysis.  In  the  first  place,  many  of  the  forms  just 
mentioned  present,  instead  of  a  single  epiphyseal  process,  two 
well-marked  structures  projecting  dorsad  from  the  roof  of  the 
interbrain.  Ontogenetically,  both  of  these  processes  are  con- 
nected with  the  epiphyseal  anlage,  and  yet  if  one  of  them  were 
called  the  epiphysis  which  should  it  be  and  by  what  term  should 
the  other  be  designated? 

In  a  certain  respect  the  suggestion  of  Hill  ('91) 179  to  call  one 
process  the  anterior  epiphysis  and  the  other  the  posterior  epiphysis 
has  much  to  recommend  it  on  morphological  grounds.  Unfor- 
tunately, connotation  has  so  rigidly  associated  the  term  epiphysis 
with  the  much  altered  and  modified  conditions  as  they  occur  in 
man  and  mammals,  as  almost  certainly  to  lead  to  confusion  in 
the  broader  application  proposed  by  Hill.  More  available, 
although  not  without  their  defects,  are  the  proposals  of  Studnicka 
(J96)386  according  to  which  the  posterior  epiphyseal  process 
becomes  the  pineal  organ  and  the  anterior  process  the  parapineal 
organ.  The  use  of  the  term  pineal  at  once  reverts  to  the  mam- 
malian forms,  for  description  of  which  it  was  first  employed. 
To  apply  this  term,  as,  for  example,  in  the  fish  where  it  has  no 
descriptive  value,  cannot  be  in  accord  with  the  best  morphologi- 
cal tendencies.  Yet  to  Studnicka  should  be  accredited  the  most 
thorough  and  extensive  consideration  of  this  subject;  his  defini- 
tions may,  for  this  reason,  be  regarded  as  standards,  especially 
if  the  desire  to  avoid  new  terms  is  kept  in  mind.  Accepting 
Studnicka's  terminology  of  an  anterior  process,  the  parapineal 
organ,  and  the  posterior  one,  the  pineal  organ,  it  is  necessary  to 
recognize  certain  subdivisions  in  each  of  these  organs.  The 
pineal  organ  has  an  end-sac,  a  stalk,  and  a  proximal  portion,  the 
latter  in  some  cases  is  connected  with  the  rest  of  the  interbrain 


THE    PINEAL    BODY  9 

by  means  of  a  short,  slightly  constricted  piece,  the  peduncle. 
The  parapineal  organ,  likewise,  has  an  end-sac,  a  stalk,  and  a  less 
well  denned  proximal  portion.  Much  variation  exists  in  the 
forms  presenting  these  several  parts — in  many  instances,  one  or 
more  of  the  parts  described  may  be  absent,  yet,  to  make  the 
terminology  as  comprehensive  as  possible,  all  of  these  portions 
should  be  included.  Upon  this  basis  the  following  constituents 
may  be  recognized  in  the  epiphyseal  complex: 

I.  The  pineal  organ,  consisting  of: 

1.  An  end- vesicle.  3.  A  proximal  portion. 

2.  A  stalk.  4.  A  peduncle. 

II.  The  parapineal  organ,  consisting  of: 

1.  An  end- vesicle.  3.  A  proximal  portion. 

2.  A  stalk. 

The  proximal  portion  and  peduncle  of  the  pineal  organ  cor- 
respond to  the  epiphysis  or  corpus  pineale  of  mammalian  anat- 
omy. The  proximal  portion  is  probably  analogous  to  the  cellu- 
lar part  of  the  pineal  body  while  the  peduncle  is  comprised 
largely  of  nerve  fibers. 

3.  GENERAL  REVIEW  OF  THE  LITERATURE 

Galen  (1576)138  gave  a  description  of  the  conarium  in  its  rela- 
tion to  the  third  ventricle  as  well  as  to  the  chorioid  plexus  and 
blood  vessels  about  it.  According  to  his  interpretation,  the 
organ  serves  as  the  support  for  the  great  vessels  converging  upon 
that  portion  of  the  brain.  Oribasius  (1554)285  mentioned  but 
did  not  describe  the  epiphysis.  Uvarthonus401  believed  that 
delicate  nerve  fibers  enter  the  pineal  body;  these  fibers  seem  to 
take  origin  in  the  lower  portion  of  the  spinal  cord.  Bauhinus 
(1616)16  considered  the  conarium  to  be  a  glandular  structure 
related  to  the  chorioid  plexus.  Diemerbroeck  (1633) 91  showed 
certain  differences  between  the  pineal  body  in  man  and  in  other 
mammals.  Dionis  (1706) 93  described  the  pineal  body  as  attached 
upon  either  side  to  the  chorioid  plexus  by  a  small  band.  This 
band  may  be  a  nerve  derived  from  the  sympathetic  system. 


10  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

Duverney  (1761) ,100  in  support  of  the  theory  of  Descartes  (1649),89 
claimed  that  the  pineal  body  did  not  exist  in  the  dog.  Vicq- 
d'Azyr  (178 1)408  observed  the  epiphysis  in  man,  but  could  not 
find  it  in  fish.  Stannius373  found  it  in  all  species  which  he  ex- 
amined and  made  a  particular  study  of  it  in  the  salmon.  In 
this  form  he  spoke  of  it  as  a  highly  vascular  structure.  Perrault306 
found  the  epiphysis  in  the  ostrich.  Borrich  and  Harder38 
observed  the  pineal  body  in  the  eagle.  Malacarne258  found  the 
epiphysis  in  birds  as  did  Cuvier  ('45). 77  Bichat  (1802) 28  con- 
sidered the  pineal  body  a  gland,  and  in  it  he  found  granules  of 
some  calcareous  substance.  The  general  character  of  the 
pineal  body  is  something  like  the  cortical  substance  of  the  brain. 
Soemmering  (1785) 359  gave  an  accurate  account  of  the  form  of 
the  conarium  and  also  its  dimensions  in  man.  In  his  descrip- 
tion he  confines  himself  largely  to  the  fact  that  there  occur  in 
the  organ  accumulations  of  a  substance  which  he  calls  brain  sand 
or  acervulus  cerebri.  Soemmering  noted  many  different  condi- 
tions under  which  this  brain  sand  was  apt  to  collect  in  the  dif- 
ferent parts  of  the  pineal  body.  Haller  (1768) 165  believed  the 
concretions  were  pathological  and  related  to  mental  disorders. 
Many  observers  made  mention  of  calcareous  concretions  in  the 
pineal  body,  among  them  being  Saltzmann,  Ruysch,  Meibomius, 
Vieussens,  Vicq-d'Azyr,  Malacarne,  Brunner,  Kruger,  Bartholin, 
Winslow,  Petermann,  and  Santorini.  Parisini300  described  the 
pineal  body  in  the  camel,  elephant,  and  lion,  and  Harder170  gave  a 
description  of  it  in  the  dog.  Carus  (1814) 59  described  the  epi- 
physis as  having  the  form  of  a  small  peeked  sac  with  almost  no 
nerve  fibers  in  it.  He  was  unable  to  find  the  organ  in  the  sal- 
mon. Chaussier63  described  the  form  of  the  pineal  body  in  some 
mammals,  suggesting  that  its  shape  compared  to  the  pomme  de 
pin,  which  comparison  led  eventually  to  the  adoption  by  the 
French  of  the  term  corpus  pineale.  The  Wenzels  (1812), 42°  in 
their  description  of  the  pineal  body,  call  attention  to  the  fact 
that  the  organ  varies  greatly  in  size  according  to  the  period  of 
life.  Its  size  from  the  seventh  year  is  augmented  regularly 
until  middle  life  and  then  a  successive  diminution  occurs  until 
old  age.  Acervulus  cerebri  is  not  found  in  the  embryo  nor  in 


THE    PINEAL   BODY  11 

the  fetus,  but  after  the  seventh  year  of  life  this  element  makes 
its  appearance  and  tends  to  increase  until  old  age.  Cruveilhier,72 
in  his  description  of  the  conarium,  drew  attention  to  a  cavity 
situated  near  the  base  of  the  structure  which  frequently  con- 
tained a  fluid.  Gratiolet,157  referring  to  this  cavity,  described 
it  as  the  ventricle  of  the  pineal  gland. 

Ma jen die,  (1795)257  commenting  at  considerable  length  upon 
the  hypothesis  of  Descartes  concerning  the  seat  of  the  soul, 
ingenuously  remarks  that  he  himself  has  a  better  conception  of 
the  nature  and  function  of  the  pineal  body  which  he  desires  to 
substitute  for  the  theory  of  Descartes.  His  own  suggestion, 
says  Majendie,  is  not  only  very  simple,  but  actual  and  true,  for 
it  must  be  obvious  from  the  situation  as  well  as  from  the  struc- 
ture and  form  of  the  pineal  body  that  it  serves  as  a  tampon 
designed  to  expand  and  in  this  way  to  close  off  the  aqueduct  of 
Sylvius  or,  at  other  times,  shrinking,  to  permit  this  aqueduct  to 
open  again  so  that  the  fluid  in  -the  ventricles  may  have  free 
access  from  the  third  chamber  to  the  fourth.  Majendie,  how- 
ever, does  not  state  upon  what  grounds  the  internal  structure  of 
the  pineal  body  justifies  such  a  belief,  but  he  is  none  the  less 
emphatic  in  calling  attention  to  the  valve-like  nature  of  the 
conarium  with  reference  to  the  cerebrospinal  fluid. 

Gunz  (1753) 161  attributed  dementia  to  impeding  of  the  flow  of 
spirits  caused  by  the  pineal  body.  Burdach  ('19-'26)4S  con- 
sidered the  pineal  body  as  supplementary  to  both  the  cerebellum 
and  cerebral  hemispheres.  Tiedemann  ('23) 395  found  the  epi- 
physis  in  reptiles,  birds,  and  mammals.  Serres  ('24-'28)353  and 
Willis429  both  make  the  statement  that  the  epiphysis  occurs  in 
fish,  birds, 'and  reptiles — in  fact,  in  all  classes  of  vertebrates. 
Andral  ('29) 4  also  described  the  organ  as  occurring  in  all  the 
classes  of  vertebrates.  Brandt  ('29) 40  recognized  a  glandular 
structure  under  a  small  scale  in  the  head  of  Lacerta  agilis  which 
corresponded  to  a  circular  depression  in  the  parietal  region  of 
the  skull.  This  he  regarded  as  a  special  gland.  Milne-Edwards 
('29), 107  in  his  researches  on  lizards,  figures  but  does  not  describe 
certain  plaques  in  the  head  of  these  animals.  He  indicates  these 
as  the  occipital  plaque,  the  parietal  plaque,  and  the  interparietal 


12  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

plaque.  The  latter  is  a  black  spot  corresponding  exactly  to  the 
position  of  the  pineal  gland.  Duges  ('29) 97  also  figures  the 
same  appearance  in  certain  lizards.  As  early  as  1835  Hollard188 
had  made  the  observation  that  the  epiphysis  was  entirely  nerv- 
ous in  structure.  He  is  also  authority  for  the  statement  that 
this  body  does  not  occur  in  fish.  Gottsche  ('35), 154  however, 
states  that  the  pineal  body  does  exist  in  all  fish.  Valentin  ('43)403 
concurred  in  Hollard' s  idea,  although  he  was  of  the  opinion  that 
the  elements  in  the  pineal  body  differed  considerably  from  the 
gray  matter  of  the  brain.  Guillot  ('84)16°  makes  the  statement 
that,  although  the  pineal  body  exists  in  all  vertebrates,  it  is  not 
until  the  reptiles  are  reached  that  the  pineal  apparatus  makes 
its  appearance  in  most  complete  form.  Reguleas  ('45) 325  recog- 
nized that  in  man  the  pineal  body,  both  in  its  volume  and  form, 
was  variable. 

.  Observations  concerning  the  structural  character  of  the  pineal 
body  were  made  at  a  remarkably  early  period.  It  was  not, 
however,  until  the  methods  of  histological  technique  were  fairly 
well  advanced  that  much  attention  was  devoted  to  the  minute 
structure  of  the  conarium.  Kolliker  ('87) 212  observed  two 
types  of  cells  in  the  pineal  body;  that  is,  small  round  cells  and 
multipolar  nerve  cells  with  compact  bundles  of  nerve  fibers. 
These  latter  were  few  in  number.  From  his  observation  Kolliker 
was  led  to  believe  that  the  pineal  body  is  entirely  nervous  in  type. 
Clarke  ('60) 69  found  nerve  fibers,  nuclei,  and  brain  sand  but  no 
nerve  cells  in  the  pineal  body.  He  also  observed  a  reticular 
structure  which  resembled  the  olfactory  mucous  membrane. 
The  arrangement  of  the  cells,  he  believed,  was  similar  to  that  of 
the  fourth  layer  of  the  olfactory  bulb  in  sheep  and  cats. 

Faivre  ('55) 114  was  among  the  first  to  make  an  extensive  com- 
parative histological  study  of  the  pineal  body.  He  examined  the 
minute  structure  in  man,  horse,  guinea-pig,  dog,  ox,  rabbit,  pig, 
hen,  turkey,  dove,  and  tortoise.  As  a  result  of  his  observations, 
he  recognized  three  elements  in  the  human  pineal  body:  first,  a 
fibro vascular  envelope;  second,  a  globular  parenchyma,  and, 
third,  acervulus  cerebri.  Faivre  is  in  general  accord  with 
Valentin,  in  that  the  pineal  body  differs  essentially  from  the 


THE    PINEAL    BODY  13 

rest  of  the  nervous  system  and  has  an  appearance  strikingly 
ike  the  pituitary  gland.  He,  apparently,  was  first  to  recognize 
that  the  cells  of  the  epiphysis  contained  granules  in  their  cyto- 
plasm. These  he  called  parenchymal  cells.  He  also  observed 
that  these  cells  were  smaller  in  childhood  than  in  adult  life  and 
concluded  that  the  parenchyma  of  the  pineal  body  is  composed 
of  a  large  number  of  globules.  The  globules  are  generally 
elliptical  and  irregular  in  shape.  Faivre  believed  the  globules 
to  be  the  nuclei  of  the  cells,  and  to  him  must  be  accredited  the 
first  observation  of  these  cellular  characteristics  of  the  pineal 
body. 

Marshall  ('61) 261  made  some  observations  concerning  size, 
\veight,  and  sand-content  in  a  chimpanzee.  Schmidt  ('62)347B 
showed  the  continuity  of  the  epiphysis  with  the  brain  in  the 
human  fetus  and  its  relation  as  an  evagination  of  the  encephalic 
roof.  Stieda  ('69) 376  studied  the  pineal  body  of  birds  and  mam- 
mals and  described  anastomoses  of  the  cytoplasm  of  the  cells 
in  the  form  of  a  reticulum.  Luys  ('65)253  advances  an  ingenious 
conception  concerning  the  nature  and  connections  of  the  pineal 
body.  In  his  opinion,  this  organ  is  a  mass  of  gray  substance 
pertaining  to  the  central  gray  matter  surrounding  the  third 
ventricle  and  having  the  same  histological  characters.  He 
claims  that  originally  in  the  human  embryo  the  structure  is 
bilobed  like  the  mammillary  bodies  and  that,  therefore,  it  should 
be  considered  as  a  transitory  bilobed  structure,  a  true  posterior 
mammillary  body  which  has  fused  across  the  median  line.  Luys 
concludes  that  the  gray  substance  of  the  conarium,  the  hippo- 
campal  convolution,  and  the  mammillary  tubercles  form  with 
the  anterior  pillars  of  the  f ornix  a  complete  system.  The  mammil- 
lary bodies  and  the  conarium  are  centers  of  reception  for  fibers 
convergent  from  the  hippocampal  convolution.  Efferently  these 
centers  are  connected  with  the  optic  thalami.  Luschka  ('67) 255 
noted  the  presence  of  fibers  in  the  pineal  body  of  man.  Frey 
('67) m  believed  that  the  pineal  body  was  made  up  exclusively 
of  nerve  tissue.  He  found  in  the  adult  the  following  elements: 
1)  multipolar  ganglionic  cells;  2)  round  cells  with  prolongations, 
and  3)  isolated  nerve  tubes.  Leydig  ('68) 232  states  that  the 


14  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

pineal  body  in  the  mouse  resembles  the  pituitary  body  in  reptiles 
with  certain  small  differences.  Meynert  (77) 271  expresses  the 
opinion  that  the  parallelism  between  the  pineal  body  and  the 
pituitary  body  is  a  mistaken  idea.  He  believes  that  the  epi- 
physis  should  be  considered  a  ganglionic  derivative  of  the  teg- 
mentum.  It  contains  two  types  of  cells,  namely,  those  with  a 
diameter  of  15  micra  and  those  with  a  diameter  of  6  micra.  The 
pineal  body,  in  Meynert's  opinion,  differs  from  other  ganglia 
only  in  the  fact  that  the  cells  are  very  close  together.  Krause 
(76) 218  observed  in  the  pineal  body  nerve  fibers  having  a  double 
contour.  Henle  (71) 171  described  the  parenchyma  of  the  pineal 
body  as  subdivided  by  fibrous  processes  called  septa  such  as 
occur  in  lymph  glands.  These  divisions  gave  rise  to  more  or 
less  independent  follicles  or  acini  varying  in  size  from  6  micra  to 
30  micra  in  diameter.  It  was  Henle's  opinion  that  the  pineal 
body  resembles  more  exactly  lymph  glands  than  any  other 
tissue  in  the  body.  Stieda  ('65) 375  in  several  species  of  amphibia 
observed  an  epithelial  structure  between  the  eyes  in  the  frontal 
region  of  the  head  which  he  called  the  frontal  cutaneous  gland. 
Subsequent  investigation  revealed  that  this  so-called  cutaneous 
gland  was  in  fact  a  portion  of  the  epiphyseal  complex.  Paw- 
lowsky  (74)305  described  fibers  in  the  epiphysis  which  seemed  to 
be  derived  from  the  posterior  commissure.  Huxley  (76) 191 
described  the  pineal  body  in  Ceratodus  forsteri.  In  this  form 
it  occurs  as  a  slender,  cylindrical  body.  Baudelot  (70) 14  gave 
a  detailed  description  of  the  pineal  body  in  Gadus  merlangus. 
He  also  found  it  in  the  salmon  and  in  the  Cyprinoids.  Camper,55 
although  he  observed  it  in  many  fish,  was  not  able  to  find  it  in 
haddock  or  cod.  Arsaky8  was  unable  to  detect  the  pouch  of 
the  pineal  body  in  fish.  Haller  (1768) 165  did  not  observe  the 
pineal  body  in  birds  nor  did  he  observe  it  in  the  pike  or  trout. 
He  did  find  it,  however,  in  the  carp  and  tench. 

Owen's  ('81) 293  view  of  the  conariohypophyseal  organs  is  such 
that  it  at  least  deserves  comment,  if  only  as  a  historical  curiosity. 
Accord'ng  to  Owen,  the  central  nervous  system  in  annelids  forms 
a  ring  through  which  passes  the  oesophagus  (cesophageal  ring). 
In  higher  vertebrates,  especially  in  embryonic  life,  the  nervous 


THE    PINEAL   BODY  15 

system  manifests  this  same  disposition,  for  here  the  brain  curves 
itself  backward  in  such  a  way  as  to  constitute  a  ring  above  the 
region  destined  to  become  the  mouth,  thus  producing  a  deep 
fossa  directed  toward  the  brain.  Owen  regards  this  as  part  of  a 
canal  which  traverses  the  brain,  now  disposed  as  the  cesophageal 
ring  of  articulates.  Early,  however,  the  process  is  arrested  and 
the  tube-like  invagination  comes  to  form  the  pituitary  gland. 
The  original  tube  from  the  mouth  region  is  completed  by  an 
invagination  from  the  dorsal  region  of  the  head  which  is  con- 
nected with  the  skin.  This  element  becomes  atrophic  and  its 
remains  constitute  the  pineal  gland.  Baraldi  ('84) 13  modified 
the  theory  of  Owen  by  stating  that  the  hypophysis  was  a  deriva- 
tive of  the  wall  of  the  mouth  of  the  gastrula  or,  in  other  words, 
the  last  vestige  of  the  extreme  anterior  portion  of  the  alimentary 
canal  of  worms.  Robin's334  idea  seemed  to  offer  some  confirma- 
tion to  this  opinion  in  the  fact  that  he  found  in  the  epiphysis, 
upon  microscopic  examination,  a  follicular,  gray  substance  con- 
taining a  granular  liquid  very  similar  to  that  in  the  intestines. 
Schwalbe  ('81)348  found  medullated  nerve  fibers  which  ac- 
company the  blood  vessels  and  come  into  relation  with  bipolar 
and  multipolar  cells  in  the  pineal  body.  He  believes  there 
existed  some  similarity  between  the  pineal  body  and  lymph 
corpuscles,  but  regards  the  cells  of  the  former  to  be  modified 
epithelial  elements.  Ganser  ('82) 142  thought  the  pineal  body  to 
be  an  unpaired  process  of  the  ganglion  habenulae.  Flechsig 
('83) m  maintained  that  the  epiphysis  sends  fibers  to  the  fascicu- 
lus retroflexus.  Sappey  ('87) 344  considered  the  pineal  body 
analogous  to  the  substance  of  the  cerebral  cortex.  Mingazzini 
('89) 276  regarded  the  elements  of  the  pineal  body  as  similar  to 
those  of  the  lymphatic  corpuscles.  Holler  ('90), 278  investigat- 
ing the  epiphysis  in  the  chimpanzee,  distinguishes  an  unpaired 
peduncle  which  constitutes  the  largest  part  of  the  pineal  body. 
The  organ  itself  is  3  mm.  x  2  mm.  long.  The  peduncle  is  4  mm. 
long  and  consists  of  nervous  tissue.  The  pineal  recess  is  ex- 
tensive. Moller  regards  the  structure  as  a  rudimentary  organ 
in  a  retrograde  state.  Charpy  ('94) 62  considers  the  epiphysis  as 
a  degenerating  organ  made  up  exclusively  of  epithelial  elements 


16  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

and  some  nerve  fibers.  Debierre  ('94) 84  believes  the  pineal 
body  to  be  a  blood  vascular  gland  with  many  degenerated 
elements.  Lotheissen  ('94)25°  studying  a  large  number  of  mam- 
mals, recognized  in  marsupials  (Macropus  giganteus)  some 
fibers  of  the  fasciculus  retroflexus  which  penetrate  the  pineal 
body,  also  some  fibers  which  leave  the  summit  of  the  epiphysis 
which  he  believes  represent  the  remains  or  rudiment  of  the 
parietal  nerve  in  reptiles.  Cajal  ('95) 53  thinks  that  the  nerve 
fibers  in  the  pineal  body  are  sympathetic  and  the  body  itself 
is  a  blood  vascular  gland.  Condorelli-Francaviglia  ('95) 70  in 
studying  the  brain  of  a  marsupial  (Halmaturus  dorsalis),  noted 
in  consequence  of  poor  development  of  the  corpus  callosum  that 
the  pineal  body  was  only  2  mm.  long  and  1.5  mm.  wide.  Heitz- 
mann  ('96)169B  described  the  epiphysis  as  composed  of  gray 
substance.  Staderini  ('97) 372  investigated  the  development  in 
many  mammals.  Soury  ('99) 365  described  connective  tissue 
septa  dividing  the  pineal  body  into  compartments  which  are 
occupied  by  a  second  tissue  resembling  adenoid  tissue  in  which 
are  round  cells  and  cells  with  long  prolongations.  Bechterew 
('00) 20  found  evidence  of  nerve  fibers  passing  from  the  posterior 
commissure  to  the  peduncle  of  the  pineal  body.  Zancla  ('06) 432 
studied  the  histology  of  the  epiphysis  in  man.  He  observed 
cells  in  the  parenchyma  which  consist  of  a  scant  protoplasm  and 
large  nuclei.  These  cells  have  a  stellate  form  and  prolongations 
which  often  bifurcate  at  acute  angles  and  then  ramify  still 
further.  The  cells  lie  in  a  mesh  of  fibrils  apparently  nervous 
in  character.  By  the  methods  of  Cajal,  Weigert,  and  Biondi, 
he  was  unable  to  interpret  these  cells  either  as  nerve  elements 
or  as  glandular  cells.  He  believed  they  are  of  a  neuroglial 
character  and  advances  the  hypothesis  that  they  have  an  internal 
secretory  function.  Around  the  calcareous  concretions  he  found 
necrobiotic  areas.  Romiti  ('82) 336  studied  the  development  of 
the  epiphysis  in  the  rabbit.  Anglade  and  Ducos  ('08) 5  found 
the  organ  made  up  mostly  of  neuroglia  in  man. 


THE  PINEAL  BODY  17 

4.  THE  COMPARATIVE  MORPHOLOGY  OF  THE  PINEAL  REGION  ; 

To  make  the  proper  evaluation  of  the  pineal  body  this  organ 
should  be  considered  in  relation  to  its  immediate  encephalic 
environment.  Indeed,  any  study  of  the  pineal  organ  which 
omitted  this  environment  would  give  but  an  inadequate  view  of 
the  epiphysis.  A  number  of  structures  make  ttieir  appearance 
in  connection  with  the  roof -plate  of  the  forebrain.  Some  of  these 
have  a  marked  constancy;  some  are  transitory,  making  their 
appearance  in  one  or  two  classes  of  vertebrates  only,  yet  all  'of 
them  have  a  definite,  phylogenetic  significance  in  connection 
with  the  epiphyseal  complex.  Embryologically,  the  roof-plate 
of  the  primitive  forebrain  vesicle,  that  is,  the  prosencephalon, 
gives  rise  to  a  number  of  evaginations.  Certain  of  these  even- 
tually become  prominent,  adult  organs.  The  most  conspicuous, 
both  because  of  its  constancy  throughout  the  phylum  and 
its  numerous  adaptations,  is  the  pineal  or  epiphyseal  complex. 
It  has  been  suggested  that  the  structures  which  form  the  roof 
of  the  interbrain  be  known  collectively  as  the  pineal  region. 
This  suggestion  made  by  Minot  ('01)m  offers  a  convenient  term 
for  the  identification  of  a  complex  area  of  the  brain.  According 
to  Minot,  the  pineal  region  begins  at  the  lamina  terminalis  or 
lamina  neuroporica  which  is  its  cephalic  limit  and  comprises  the 
following  elements: 

1.  The  paraphyseal  arch. 

2.  The  velum  trans ver sum. 

3.  The  post  velar  arch,  also  known  as  the  dorsal  sac. 

4.  The  epiphysis,  also  known  as  the  corpus  pineale. 

5.  The  posterior  commissure. 

Minot 's  specification  of  the  pineal  region  needs  some  extension 
in  order  to  meet  the  requirements  of  all  classes  of  vertebrates. 
The  following  description  of  the  pineal  region  makes  provision 
for  all  of  the  elements  which  may  and  in  some  instances  do 
appear  in  this  area  of  the  brain. 

Paraphysis.  The  paraphysis  is  an  evagination  situated  at 
the  extreme  cephalic  end  of  the  forebrain  roof-plate.  Ventrally 
it  is  continued  into  the  lamina  neuroporica.  Dorsally  it  is  con- 
tinuous with  the  velum  transversum.  Minot  assumed  that  the 


MEMOIR  9 


18  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

pineal  region  develops  a  series  of  structures  which  seem  to  be 
directly  concerned  with  the  formation  of  the  fluid  in  the  cavities 
of  the  brain.  He  holds  that  the  chorioid  plexus  supplies  the 
main  bulk  of  this  fluid,  but  the  gland-like  organization  of  the 
paraphysis  indicates  that  it  may  supply  a  secretion  of  special 
chemical  substances  to  the  encephalic  fluid.  The  organ  reaches 
its  highest  degree  of  development  in  amphibia,  where  it  becomes 
a  large,  complicated,  glandular  structure  with  a  central  canal 
from  which  a  complicated  set  of  anastomosing  tubules  are  given 
off.  It  has  a  well-marked  sinusoidal  type  of  circulation.  These 
conditions  have  been  observed  by  Warren416  in  Siredon,  Nec- 
turus,  Proteus,  Siren,  Ichthyophis,  Triton,  Rana,  Amblystoma, 
and  Diemyctylus.  The  paraphysis  has  a  well-developed, 
glandular  character  in  amphibians  and  lizards;  in  birds  it  is 
reduced  to  a  single,  thick-walled  outgrowth  of  small  dimensions. 
Selenka352  in  1890  observed  the  organ  in  opossum;  it  has  also 
been  observed  by  Warren  ('17)417  in  the  sheep,  and  also  by 
Francotte127  in  1887  in  the  human  embryo.  The  paraphysis  is 
much  reduced  in  the  upper  and  lower  ends  of  the  vertebrate 
series,  while  in  the  middle,  especially  in  amphibia,  it  is  much 
developed.  In  amphibia  its  character  is  glandular,  as  it  is  also, 
to  a  less  degree,  in  reptiles. 

The  paraphysis  was  erroneously  regarded  as  the  conarium  by 
Selenka  ('90). 352  It  has  also  been  called  the  anterior  epiphysis 
by  Burckhardt  ('90)42  and  the  pre-paraphysis  by  His  ('68). 182 
Sorensen  ('94), 363  called  it  the  posterior  chorioid  plexus. 

The  velum  transversum.  This  is  a  transverse  furrow,  imme- 
diately caudad  to  the  paraphysis,  which  projects  into  the  ventricle 
and  separates  the  paraphysis  from  the  dorsal  sac.  In  some 
instances  this  furrow  is  simple  and  flat,  but  in  others  it  is  thrown 
into  many  subsidiary  folds  and  becomes  highly  vascular  in  the 
form  of  a  plexus.  In  some  forms,  as  in  Peiromyzon,  it  is  alto- 
gether wanting,  and  under  such  circumstances  the  paraphysis 
passes  over  without  sharp  line  of  demarcation  directly  into  the 
dorsal  sac.  In  Chimaera  there  is  a  lack  of  the  velum  and  also 
a  small  paraphysis  so  that  the  dorsal  sac  seems  to  pass  over 
into  the  lamina  supraneuroporica  without  demarcation.  In 


THE    PINEAL   BODY  19 

Dipnoians  the  velum  presents  a  pair  of  folds  or  it  may  develop, 
as  in  certain  amphibia,  as  an  unpaired  chorioid  plexus. 

The  dorsal  sac.  This  element  of  the  pineal  region  was  called 
the  Zirbelpolster  by  Burckhardt42  in  1890,  the  parencephalon 
by  Kupffer222  in  1887,  and  the  post-paraphysis  by  Sorensen362 
in  1893.  Goronowitsch  ('88) 153  appears  to  be  the  first  to  apply 
to  it  the  term  dorsal  sac.  This  sac  is  a  dilated  vesicle  usually 
extending  far  above  the  roof-plate.  In  mammalia,  however, 
in  those  forms  in  which  the  corpus  callosum  has  made  its  appear- 
ance, the  sac  becomes  much  flattened  and  is  difficult  to  recognize 
because  of  the  altered  condition  consequent  upon  the  develop- 
ment of  the  corpus  callosum.  The  walls  of  the  dorsal  sac  are 
lined  internally  by  ependymal  cells.  In  many  instances  these 
walls  may  be  thin  and  definite  or  quite  thick,  containing  many 
folds  which  may  or  may  not  be  vascular;  in  certain  instances 
these  folds  attain  such  a  vascularity  that  they  resemble  a  chorioid 
plexus. 

The  pars  intercalaris  anterior.  The  more  caudal  portion  of 
the  dorsal  sac  as  it  approaches  the  level  of  the  roof-plate  may 
become  much  thickened  and  contain  a  dense  mass  of  neuroglia 
tissue.  Usually  this  intercalated  portion  is  not  of  any  great 
extent.  It  appears  only  in  a  few  forms. 

The  commissura  habenularis.  This  element  was  called  by 
Osborn288  in  1884  the  superior  commissure  and  by  Gottsche  in 
1835154  the  commissura  tenuissima.  It  affords  a  connection 
between  the  two  ganglia  habenulae.  In  some  cases,  as  in  Petro- 
myzon,  the  connection  established  by  this  commissure  is  such  as 
to  include  the  mass  of  the  two  ganglia  in  the  general  commissural 
region.  In  the  immediate  neighborhood  of  this  commissure  and 
coming  into  direct  connection  with  it  is  often  seen  the  ending  of 
the  nerve  from  the  parapineal  organ.  This  is  particularly  the 
case  in  Saurians,  and  it  is  by  tnis  means  that  the  so-called  parietal 
nerve  makes  its  connection  with  the  brain.  Its  fibers  may  be 
traced  in  some  instances  as  far  as  the  ganglia  habenulae. 

The  epiphyseal  complex.  This  complex  comprises  two  distinct 
elements,  a  pineal  and  a  parapineal  organ.  The  pineal  organ 
may  consist  of  an  end-sac  or  terminal  vesicle,  a  stalk,  a  proximal 


20  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

portion,  and  a  peduncle.  In  all  probability  the  proximal  por- 
tion of  the  epiphyseal  complex  gives  rise  to  the  epiphysis  cerebri 
or  what  has  been  called  the  pineal  gland.  In  some  forms  nerve 
fibers  have  been  found  making  their  course  through  the  stalk  of 
this  pineal  organ  and  have  thus  given  rise  to  the  term  nervus 
pinealis.  The  parapineal  organ  is  the  second,  though  less  con- 
stant, portion  of  the  epiphyseal  complex.  When  present,  it  also 
consists  of  an  end-vesicle,  a  stalk,  and  a  somewhat  dilated 
proximal  portion.  Most  of  these  evaginations  contain  cavities 
which  are  in  communication  with  the  third  ventricle.  The 
recess  which  connects  the  pineal  organ  with  this  ventricle  is 
known  as  the  recessus  pinealis. 

.  The  pars  intercalaris  posterior.  The  caudal  wall  of  the  proximal 
portion  of  the  pineal  organ  often  shows  a  marked  increase  in 
thickness  as  it  approaches  the  level  of  the  diencephalic  roof. 
This  thickening  interposes  an  area  between  the  proximal  portion 
of  the  pineal  organ  and  the  posterior  commissure.  Often  this 
intercalated  part  shows  considerable  dimensions.  In  the  forms 
in  which  it  is  most  developed,  the  fibers  of  the  pineal  nerve  may 
be  seen  to  enter  this  intercalated  portion  in  the  roof  of  the  inter- 
brain.  It  has  been  called  the  pars  intercalaris  by  Burckhardt 
in  1890,42  but  the  necessity  of  designating  it  the  posterior  inter- 
calated portion  becomes  obvious  in  view  of  the  fact  that  an 
anterior  structure  of  like  character  has  already  been  described. 

The  posterior  commissure.  The  last  and  caudalmost  struc- 
ture in  the  roof  of  the  interbrain  is  the  posterior  commissure. 
This  has  already  been  assigned  by  Minot  in  1901277  to  the  mid- 
brain,  but  the  fact  'that  certain  fibers  from  the  tractus  pinealis 
and  the  nervus  pinealis  may  be  traced  into  direct  relation  with 
this  commissure  seems  to  ally  it  more  with  the  derivatives  of  the 
roof-plate  in  the  interbrain  region  rather  than  that  of  the  mesen- 
cephalon. 

The  homology  of  all  of  these  parts  in  the  roof -plate  of  the 
prosencephalon  has  been  given  for  the  different  classes  of  verte- 
brates by  Burckhardt  in  189042  in  his  work  on  Protopterus  and 
again  in  his  work  (45)  on  the  structural  plan  of  the  brain.  With 
this  view  of  the  generalized  plan  of  the  pineal  region  in  verte- 


THE    PINEAL   BODY  21 

brates,  it  will  now  be  possible  to  consider  in  detail  some  of  the 
variations  which  the  region  presents  in  the  different  classes. 

1 .  The  pineal  region  in  cyclostomes 

In  cyclostomes  the  absence  of  the  velum  transversum  causes 
the  paraphysis  to  pass  over  into  the  dorsal  sac  without  sharp 
line  of  demarcation.  In  fact,  it  is  difficult  to  make  out. with 
any  degree  of  certainty  a  true  paraphyseal  process.  What 
there  is  of  a  paraphysis  is  a  small  evagination  from  the  most 
cephalic  portion  of  the  dorsal  sac,  and  the  morphological  lines  of 
differentiation  are  such  as  to  leave  it  still  open  to  doubt  whether 
there  is  an  actual  paraphysis  in  these  forms.  Studnicka  ('99) 388 
is  authority  for  the  statement  that  such  an  organ  does  exist 
in  Petromyzon.  In  Ammoccetes  the  epiphysis  is  more  clearly 
defined.  The  lamina  supraneuroporica  in  cyclostomes  is  more 
specialized  than  in  other  vertebrates.  In  the  most  dorsal  por- 
tion of  this  membrane  there  occurs  a  thickening  which  lodges 
fibers  passing  in  a  transverse  direction  and  constitutes  a  com- 
missure knbwn  as  the  commissura  pallii.  The  dorsal  sac  is  un- 
usually high  and  deflected  in  a  cephalic  direction  as  a  result  of 
the  pressure  put  upon  it  by  the  pineal  and  parapineal  organs. 
Its  dorsocaudal  wall  shows  a  marked  in  vagina  tion  as  a  result  of 
the  pressure  not  only  of  the  epiphyseal  complex,  but  also  of  the 
ganglion  habenulae.  No  chorioid  plexus  or  other  vascular  for- 
mation appears  in  direct  connection  with  either  the  paraphysis 
or  the  dorsal  sac.  The  pars  intercalaris  anterior  is  absent,  but 
a  very  massive  commissura  habenularis  is  observed  in  all  forms, 
making  its  appearance  early  in  the  course  of  development. 

The  epiphyseal  complex  presents  a  pineal  organ  and  a  para- 
pineal  organ.  Both  of  these  lie  in  close  apposition  to  each  other 
extending  cephalodorsad  in  such  a  direction  that  their  terminal 
portions  come  to  overlie  the  dorsal  sac.  The  dorsal  wall  of  the 
pineal  organ  lies  immediately  beneath  the  frontal  region  of  the 
skull.  The  posterior  intercalated  portion  is  also  absent,  but  a 
large  posterior  commissure  occurs  in  all  forms.  The  pineal,  as 
well  as  the  parapineal  organ,  possesses  a  nerve,  that  connected 


22  FREDERICK   TILNEY   AND    LUTHER   F.   WARREN 

with  the  pineal  organ,  the  so-called  pineal  nerve,  ends  in  the 
posterior  commissure,  while  the  parapineal  nerve  has  its  termi- 
nation in  the  commissura  habenularis. 

Probably  the  first  observation  upon  this  region  in  the  cyclo- 
stomes  was  made  by  Serres353  in  1825.  Other  contributions  fol- 
lowed by  Schlemm  and  d'Alton  347C  in  1838.  Johannas  Miiller280 
in  1838  and  Siebold  and  Stannius355  in  1854  added  their  studies 
of  this  region.  Mayer265  in  1864  mentioned  the  occurrence  of 

Epid         Cor 


-.Sohd 


JLs 


Fig.  1  Schematization  of  pineal  region  in  Cyclostomes,  according  to  Stud- 
nicka,  1905. 

Ls.,  lamina  terminalis ;  .P/,  paraphysis;  Pp.,  parapineal  organ  ',Po.,  pineal  organ; 
Ha.,  habenular  ganglion;  Th.,  parapineal  nerve;  Ch.,  commissura  habenularis;  R., 
recessus  pinealis;  Cp.,  commissura  posterior;  n.,  Npin.,  nervus  pinealis. 

many  calcium  corpuscles  in  and  about  the  pineal  organ.  Wie- 
dersheim422  in  1880  spoke  of  the  epiphysis  as  a  small,  saccular 
body,  but  it  was  not  until  1883  that  Ahlborn2  first  described  the 
microscopic  appearances  of  the  epiphyseal  complex  in  which 
he  was  able  to  observe  two  superposed  vesicles.  Ahlborn, 
however,  did  not  interpret  these  two  vesicles  as  independent 
evaginations  from  the  roof  of  the  interbrain,  but  considered 
them  as  subdivisions  of  the  epiphysis. 


THE    PINEAL   BODY  23 

Later,  Beard  ('87)17  and  Owsiannikow  ('88)295  following  Ahl- 
born's  lead,  both  spoke  of  two  epiphyseal  vesicles.  Studnicka 
('99) 388  and  Kupffer  ('94) 224  showed  that  these  two  vesicles  were, 
in  fact,  independent  parts  of  the  epiphyseal  complex.  Studnicka 
called  the  anterior  vesicle  the  parapineal  organ  and  considered  it 
homologous  to  the  parietal  eye  of  reptiles.  This  he  later  con- 
firmed in  a  subsequent  work.  Kupffer,  however,  saw  in  the 
parapineal  organ  or  parietal  eye  of  reptiles  the  homologue  of  the 
paraphysis  in  Petromyzon.  Retzius  ('95)331B  was  the  first  to 
employ  the  Golgi  method  in  Petromyzon  and  Ammoccetes. 
By  this  means  he  was  able  to  demonstrate  the  nerve  elements 
of  the  stalk  of  these  two  epiphyseal  organs.  The  finer  structure 
of  the  pineal  and  parapineal  organs  in  Petromyzon  marinus  was 
given  by  Leydig  in  1853231  and  Studnicka  in  1899,388  while  Johns- 
ston  in  1902195  described  these  organs  in  Lampetra  wilderi. 

2.  The  pineal  region  in  selachians 

The  pineal  region  in  selachians  is  very  similar  to  that  of 
Petromyzon  with  the  exception  that  in  the  epiphyseal  complex 
the  parapineal  organ  does  not  appear.  The  selachians  are 
remarkable  for  another  fact,  namely,  that  one  member  of  this 
class,  Torpedo,  develops  no  part  whatsoever  of  the  epiphyseal 
complex;  that  is  to  say,  both  the  pineal  and  parapineal  organs 
are  wanting. 

In  Notidanus,  Burckhardt  in  189042  distinguishes  the  follow- 
ing parts:  At  the  dorsal  extremity  of  a  thickened  and  invagi- 
nated  lamina  neuroporica  there  appears  a  slightly  developed 
paraphysis.  Immediately  following  this  in  the  roof-plate  there 
is  a  marked  invagination  defining  the  velum  transversum,  which 
appears  in  these  forms  as  a  simple  infolding  of  the  roof-plate 
without  any  vascular  development.  The  dorsal  sac  presents 
itself  as  a  more  conspicuous  element  in  the  roof  of  this  species 
than  in  the  cyclostomes.  There  is  no  anterior  intercalated 
portion  and  the  epiphyseal  complex  shows  only  the  presence  of 
the  pineal  organ.  A  short  pars  intercalaris  posterior  has  been 
described  followed  by  the  posterior  commissure.  This  descrip- 
tion given  by  Burckhardt  in  Notidanus  holds  true  for  most  of 
the  forms  of  selachians  with  the  exception  of  Torpedo. 


24 


FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 


d'Erchia  ('96) 109  differentiated  in  Pristiurus  the  same  elements 
as  in  Notidanus,  but  in  Torpedo  he  found  that  the  epiphyseal 
complex  was  entirely  wanting.  He  further  observed  that  the 
development  of  the  velum  transversum  occurred  much  earlier 
than  the  pineal  organ.  Minot  ('01) 277  maintained  that  an  actual 
paraphysis  does  not  develop  in  selachians.  In  comparing  the 
pineal  regions  of  cyclostomes  with  selachians,  the  most  striking 


po— 


Ls 


Fig.  2  Schematization  of  pineal  region  in  Selachians,  according  to  Studnicka 
1905. 

Ls.,  lamina  terminalis;  P/.,  paraphysis;  V.  velum  transversum;  Ds.,  dorsal 
sac;  Po.,  pineal  organ;  St.,  stalk  of  pineal  organ;  Ch.,  commissura  habenularis; 
R.,  recessus  pinealis;  Cp.,  commissura 'posterior;  Sch.,  pars  intercalaris  posterior; 
Prox.,  proximal,  portion;  Tp.,  tractus  pinealis. 

differences  appear  to  be  in  the  extreme  development  of  the 
parapineal  and  pineal  organs  in  Petromyzon  and .  allied  forms, 
while  the  parapineal  organ  is  absent  in  selachians.  Further- 
more, the  absence  of  any  distinct  velum  transversum  in  cyclo- 
stomes makes  the  presence  of  a  definite  paraphysis  extremely 
doubtful,  while  the  velum  transversum  in  selachians  differen- 
tiates very  clearly  a  fairly  well  formed  paraphysis.  The  pineal 
region  in  Elasmobranchs  is  much  shorter  than  in  Petromyzon. 


THE    PINEAL   BODY  25 

Of  the  early  workers  upon  the  selachian  pineal  region,  Jack- 
son and  Clarke  (75) 193  appear  to  be  the  first  to  make  mention  of 
the  actual  pineal  organs  as  they  occur  in  these  forms.  They 
described  this  region  in  the  brain  of  Echinorhynus  spinosus. 
According  to  their  description,  the  structure  was  a  small  pro- 
jection extending  frdm  the  roof  of  the  interbrain  to  the  surface 
of  the  skull.  Ehlers108  in  1878  gave  the  first  detailed  description 
of  the  relation  of  these  parts  in  Acanthias  and  Raia.  Balfour 
('78) 10  in  the  same  year  described  the  embryological  development 
of  the  pineal  region  in  selachians.  Cattie  ('82) 60  gave  the  de- 
scription of  the  pineal  organ  in  a  large  number  of  Elasmobranchs. 
Carrington  ('90) 58  described  the  organ  in  Lamna  cornubica  and 
Galeotti  ('96)14°  employing  certain  cytological  methods  in  his 
investigations  of  the  pineal  region,  gave  an  important  description 
of  these  parts  from  a  histological  point  of  view.  d'Erchia's 
work  on  Pristiurus  and  Torpedo  has  already  been  referred  to. 
His  was  the  notable  observation  that  the  epiphyseal  complex 
was  entirely  absent  in  Torpedo. 

3.  The  pineal  region  in  ganoids 

This  region  in  ganoids  is  characterized  by  the  presence  of  the 
usual  elements  with  the  exception  that  the  parapineal  organ  does 
not  develop.  In  Amia  alone  is  there  any  rudiment  of  an  anterior 
portion  of  the  epiphyseal  complex,  and  even  here  it  is  so  slight 
as  hardly  to  justify  the  attempt  to  homologize  it  with  the  para- 
pineal  organ  in  Petromyzon.  Goronowitsch  ('88) 153  and  Kupffer 
('93) 223  described  the  pineal  region  in  Acipenser  and  recognized 
in  it  all  of  the  parts  usually  observed  in  this  area  of  the  brain. 
Following  a  broad  lamina  supraneuroporica  there  is  a  well- 
marked  paraphysis  which  at  first  is  truly  membranous  but  subse- 
quently becomes  highly  vascular  and  takes  on  the  form  of  a 
tubular  gland  eventually  concealing  the  great  part  of  the  lamina 
terminalis.  In  certain  forms,  as  in  Polyodon,  the  paraphysis, 
although  well  developed,  is  relatively  much  smaller  than  in 
Acipenser.  The  next  element  in  the  forebrain  roof,  namely, 
the  velum  transversum,  is  broad  and  much  convoluted  although 
not  very  highly  vascular.  The  dorsal  sac  presents  the  form  of  a 


26  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

large  evagination,  generally  membranous,  and  in  several  forms 
having  marked  prolongations.  Thus  in  Amia  there  are  two  such 
prolongations,  the  more  dorsal  of  which  extends  as  far  back  as 
the  midbrain,  while  in  Polypterus  a  prolongation  of  the  dorsal 
sac  arches  over  the  midbrain  and  extends  as  far  caudad  as  the 
cerebellum.  No  anterior  intercalated  part  is  present  in  the 
ganoid,  but  a  well-marked  habenular  commissure  is  present 
immediately  cephalad  of  the  epiphyseal  complex.  This  latter 
consists  of  a  single  evagination  from  the  roof-plate.  The  anterior 
epiphyseal  element  is  absent  in  the  ganoid  so  that  the  pineal 
organ  alone  is  encountered  in  this  region.  Immediately  follow- 
ing the  latter  structure  is  a  short  pars  intercalaris  posterior  and 
then  a  large  posterior  commissure. 

The  pineal  region  in  ganoids  differs  from  that  in  selachians 
mainly  in  the  presence  of  a  large  and  glandular  paraphysis;  also 
in  the  existence  of  an  unusually  large  and  extensive  dorsal  sac, 
prolongations  of  which  are  apt  to  extend  far  beyond  the  usual 
limits  of  this  structure,  even  arching  over  the  midbrain  and 
reaching  the  cerebellum. 

Of  the  early  works  upon  ganoids,  Salensky341  in  1881  first 
gave  a  description  of  the  development  of  the  pineal  region  in 
Acipenser.  Accounts  of  the  ontogenesis  in  this  same  form  were 
later  given  by  Owsiannikow  ('90)297  and  Kupffer  ('93). 223  Bal- 
four  and  Parker  ('82)12  gave  a  description  of  the  development  of 
this  region  in  Lepidosteus.  Hill  ('94)18°  contends  that  there  are 
two  epiphyseal  outgrowths  from  the  roof  of  the  interbrain  in 
Amia  calva.  The  more  anterior  of  these  two  outgrowths  or 
vesicles,  Hill  thinks,  is  homologous  with  the  parietal  eye  of 
Lacertilia,  and  he  further  maintains  that  it  is  extremely  prob- 
able that  the  two  vesicles  in  their  primitive  position  were  side  by 
side,  thus  indicating  the  existence  of  two  organs  which  in  the 
primitive  form,  like  the  lateral  eyes,  were  arranged  as  a  pair  for 
some  definite  function.  Eycleshymer  and  Davis  ('97) 113  con- 
firmed the  findings  of  Hill  and  added  the  further  important 
observations  that  in  the  late  embryonic  state  nerve  fibers  could 
be  seen  connecting  the  commissure  habenularis  with  the  para- 
pineal  as  well  as  the  pineal  organ. 


THE    PINEAL    BOD  Y  27 

4.  The  pineal  region  in  teleosts 

In  teleosts  the  parapineal  organ  does  not  appear  and  the 
pineal  organ  itself  is  present  only  in  a  seemingly  retrogressive 
condition.  During  the  early  stages  of  development,  however, 
in  a  few  forms  there  is  an  anlage  of  the  parapineal  organ.  The 
lamina  supraneuroporica  is,  if  anything,  more  broad  and  more 
pronounced  than  in  the  ganoids,  but  it  differs  from  this  structure 
in  the  latter  forms  in  the  fact  that  it  is  not  vascular  nor  does  it 
come  into  relation  with  any  vascular  network.  A  paraphysis 
does  not  develop,  as  a  rule,  or  if  it  does  occur,  it  only  appears 
as  a  small  evagination  from  the  roof-plate,  as  in  Belone  acus. 
Not  infrequently  in  the  earlier  stages  of  development  in  Lophius, 
the  paraphysis  appears  as  a  small  bud  in  the  roof  region.  In 
the  larval  forms  of  some  species,  as,  for  example,  Anguilla  and 
Cepola,  the  paraphysis  has  the  form  of  a  very  small  evagination 
from  the  roof  consisting  of  a  thin  wall,  but  is  not  vascular  and 
in  no  way  connected  with  a  vascular  net.  The  velum  trans- 
versum  is  a  simple,  flat,  transverse  fold  which  is  not  in  connec- 
tion with  the  chorioid  plexus  in  any  portion.  In  certain  in- 
stances this  element  is  very  little  developed  and  may,  in  a  few 
cases,  be  entirely  absent.  The  dorsal  sac  is,  as  a  rule,  very  large 
and  presents  itself  in  several  different  forms.  Frequently  it  is 
thrown  into  many  folds,  particularly  the  portion  representing 
the  superior  wall  and  in  these  folds  are  found  numerous  blood- 
vessels in  a  plexiform  arrangement.  Sometimes  the  sac  along 
its  caudal  wall  is  grooved  in  the  midsagittal  plane  and  in  this 
groove  rests  the  stalk  of  the  pineal  organ.  An  anterior  inter- 
calated portion  is  absent,  but  a  well-marked  habenular  com- 
missure is  always  observed.  Following  this  commissure  is  the 
pineal  organ  and  caudal  to  it  a  short  pars  intercalaris  posterior 
followed  by  the  posterior  commissure  (fig.  3). 

Among  the  early  workers  in  this  region  in  teleosts  are  listed 
some  of  the  great  pioneer  names  in  morphology.  Albrecht 
Haller  in  1768165  described  the  epiphysis  in  the  carp,  but  did 
not  find  it  in  the  trout.  Cuvier  in  184577  also  observed  it  in 
teleosts,  and  Carus  in  181459  found  it  to  be  a  saccular  formation 
extending  from  the  dorsal  .region  of  the  brain.  Tiedemann39^ 


28 


FREDERICK    TILNEY   AND    LUTHER   F.    WARREN 


in  1816  could  not  find  it  in  the  bony  fish,  while  Gottsche154  in 
1835  found  it  in  these  animals,  but  thought  that  it  was  connected 
by  blood  vessels  or  a  membrane  with  the  ganglion  habenulae 
and  the  commissura  habenularis.  Mayer  in  1864265  gave  a 
description  of  the  epiphysis  as  being  merely  a  vascular  convolu- 
tion in  the  roof  of  the  interbrain,  while  Owen294  in  1866  was  not 
at  all  sure  of  its  existence  even  as  a  vascular  convolution  of  the 
roof-plate.  In  1870  Baudelot14  described  the  epiphysis  as  a 


-Af 


7>-      Sc/t  Cp 

Fig.  3  Schematization  of  pineal  region  in  Teleosts,  according  to  Studnicka, 
1905. 

Ls.,  lamina  terminalis;  P/.,  paraphysis;  Ds.,  dorsal  sac ;  V.,  velum  trans versum; 
Ch.,  commissura  habenularis;  Po.,  pineal  organ;  St.,  stalk  of  pineal  organ;  Tp., 
tractus  pinealis;  Sch.,  pars  intercalaris  anterior;  Cp.,  commissura  posterior;  M. 
midbrain. 

round  or  pear-shaped  body  between  the  lobi  optici.  The  first 
exact  description  of  the  organ  was  given  by  Rabl-Riickhard319 
in  1883  on  the  basis  of  microscopic  sections.  Cattie60  in  1882 
described  the  gross  appearances  of  the  organ  in  a  large  number  of 
teleosts,  and  Hill180  in  1894  gave  one  of  the  most  detailed  and 
reliable  accounts  of  this  region  in  teleosts,  basing  his  description 
on  his  findings  in  salmon.  Other  excellent  descriptions  of  the 
organ  in  teleosts  have  been  given  by  Ussow  ('82), 402  Leydig 
(?96),239  and  Handrick  ('01). 168 


THE    PINEAL    BODY  29 

The  work  of  Galeotti140  in  1896  on  these  forms  is  of  particular 
interest.  This  observer,  applying  certain  means  of  cellular 
differentiation  in  the  -technique,  showed  that  some  cells  of  the 
pineal  organ  give  definite  evidence  of  secretory  activity.  In 
Leuciscus  he  found  that  the  nuclei  of  the  cells  contained  fuch- 
sinophile  granules  and  also  that  the  nucleoli  in  these  nuclei 
were  often  extruded  and  later  appeared  in  the  protoplasm  of  the 
cells.  The  product  of  such  secretion  in  Galeotti' s  opinion  was 
delivered  to  the  cavity  of  the  organ. 

The  chief  difference  between  the  pineal  region  in  ganoids  and 
teleosts  lies  in  the  fact  that  in  the  latter  forms  the  paraphysis  is 
entirely  absent  while  in  ganoids  it  constitutes  a  conspicuous 
element. 

5.  The  pineal  region  in  dipnoi 

In  dipnoi  the  only  portion  of  the  epiphyseal  complex  which 
develops  is  the  pineal  organ  and  this  is  much  less  well  defined 
than  in  the  lower  forms.  No  anlage  of  the  parapineal  organ 
makes  its  appearance.  The  paraphysis  develops  later  than  the 
pineal  organ.  The  lamina  supraneuroporica,  according  to 
Burckhardt  ('90), 42  as  it  appears  in  Protopterus,  is  very  thick 
and  well  developed.  The  absence  of  any  well-defined  velum 
transversum  makes  it  appear  as  if  the  paraphysis  were  an  an- 
terior division  of  the  dorsal  sac,  and  yet  a  paraphysis  may  be 
said  to  exist  in  these  forms,  although  no  sharp  line  of  demarca- 
tion may  be  drawn  between  it  and  the  dorsal  sac.  The  para- 
physis itself  presents  a  number  of  transverse  folds  beginning  in 
the  attenuated  membrane  immediately  dorsal  to  the  lamina 
supraneuroporica.  In  Ceralodus  the  entire  paraphysis  has  the 
appearance  of  a  glandular  structure,  the  lumen  of  which  is  in 
connection  with  the  ventricle  of  the  brain  by  means  of  a  small 
canal.  Although  an  actual  velum  transversum  does  not,  in  the 
strict  sense,  exist,  Kerr  ('03), 202  in  Lepidosiren,  and  Studnicka 
('95,  '96), 386  in  Ceratodus,  have  both  described  several  folds  in  a 
position  dorsal  to  the  paraphysis.  The  dorsal  sac  is  but  little 
developed,  although  it  does  appear  as  a  membranous  structure 
extending  from  the  roof  of  the  interbrain.  No  pars  intercalaris 


30  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

anterior  is  observed,  but  there  is  a  well-marked  commissura 
habenularis  as  well  as  the  pineal  organ,  a  posterior  intercalated 
portion,  and  the  posterior  commissure. 

The  earliest  work  upon  this  region  of  the  dipnoi  was  by 
Huxley191  in  1876.  In  this  he  described  the  pineal  organ  as  a 
cylindrical  structure  which  had  a  cordiform  enlargement  at  its 
distal  extremity.  This  latter  lay  deeply  seated  in  a  small  exca- 
vation of  the  cartilaginous  skull  roof.  Wilder427  in  1887  showed 
an  unusually  large  paraphysis  in  Ceratodus,  but  did  not  observe 
the  pineal  organ.  Sanders343  in  1889  saw  the  end^  vesicle  of  the 
pineal  organ  in  the  form  of  a  small  body  situated  above  the 
chorioid  plexus  of  the  interbrain.  Studnicka  ('95,  '96), 386 
distinguished  in  Ceratodus  a  dorsal  sac  and  a  paraphysis,  the 
former  lying  closely  compressed  against  the  latter.  He  also 
observed  a  pineal  organ  with  a  long  stalk  which  lies  in  a  fold 
along  the  superior  wall  of  the  dorsal  sac,  while  the  end-vesicle 
is  situated  above  the  paraphysis.  In  Protopterus  annectens, 
Wiedersheim  ('80)423  and  Beauregard  ('81) 19  mistook  the  dorsal 
sac  for  the  pineal  organ,  and  Fulliquette  ('86) 132  was  unable  to 
distinguish  between  the  ganglion  habenulae  and  the  pineal 
organ.  The  erroneous  identifications  made  by  these  authors  go 
to  show  the  great  difficulties  which  the  pineal  region  in  dipnoians 
presents.  It  was  not  until  1890  and  1892  that  Burckhardt42"44 
first  gave  the  proper  description  of  the  pineal  organ  in  these 
forms. 

6.  The  pineal  region  in  amphibia 

In  Urodela  and  Apoda  only  the  pineal  organ  develops  and 
this  in  but  an  extremely  rudimentary  form.  The  portions  of  the 
pineal  organ  which  are  present  in  these  forms  represent  the 
proximal  part  of  that  structure.  In  no  other  group  of  verte- 
brates is  the  pineal  organ  so  little  developed;  it  presents  itself  as 
a  sac  lying  close  to  the  interbrain,  the  lumen  of  which  is  sub- 
divided into  numerous  branches.  deGraaf155  in  1886  was  first 
to  recognize  this  condition  and  describe  it  in  amphibia. 

In  Anura,  as  in  Urodela  and  Apoda,  the  pineal  organ  only 
develops.  It  usually  consists  of  the  proximal  saccular  part  of 


THE    PINEAL    BODY  31 

this  structure  and  the  end-vesicle.  The  latter  constitutes  the 
cutaneous  gland.  These  two  parts,  connected  by  a  stalk  of  fine 
fibers  which  lead  to  the  brain  roof  as  the  tractus  pinealis,  are  the 
distinguishing  features  of  this  region  in  Anura.  The  proximal 
part  alone  in  Anura  is  the  homologue  of  the  very  rudimentary 
organs  observed  in  Urodela.  The  pineal  organ  of  the  frog's 
brain  has  often  been  mistaken  for  the  highly  developed  chorioid 
plexus,  for  the  paraphysis,  or  for  the  dorsal  sac.  Such  errors 
have  been  made  by  Wymann431  in  1853,  Reissner328  in  1864,  and 
Stieda379  in  1875.  Goette151  in  1873  first  recognized  the  proximal 
portion  of  the  pineal  organ  and  called  it  the  epiphysis.  This  he 
observed  in  the  early  stages  of  development  in  Bombinator. 
Gravenhearst158  many  years  before  this  found  the  distal  part  of 
the  pineal  organ  in  the  head  of  Rana  subsaltans,  situated  in 
relation  to  a  light  colored  spot  on  the  skin  over  the  head.  Reiss- 
ner328 also  noted  a  similar  spot.  Stieda  called  this  spot  the 
Scheitelfleck  (parietal  spot).  To  this  spot  he  gave  an  inter- 
pretation of  much  interest,  for  he  believed  that  it  marked  the 
situation  of  a  peculiar,  subcutaneous  frontal  gland  directly  under 
the  skin  and  this  gland,  therefore,  became  known  as  the  frontal 
subcutaneous  gland  of  Stieda.  A  fine,  thread-like  structure  led 
from  the  skull  to  this  gland  and  thus  connected  them.  Ciaccio65 
in  1867,  following  Stieda's  lead,  placed  this  structure  among  the 
so-called  nerve  glands  of  Luschka.  Leydig233  in  1856  considered 
the  organ  merely  as  a  skin  gland,  but  Goette151  in  1873-75  studied 
the  epiphysis  development  ally  and  stated  that  the  subcutaneous 
frontal  gland  was  nothing  more  than  the  detached  distal  end  of 
the  epiphysis. 

The  pineal  region  in  amphibia,  generally  speaking,  comprises 
the  following  structures:  The  lamina  supraneuroporica,  which 
is  a  short  and  thick  end  wall  of  the  forebrain.  The  next  and, 
perhaps,  most  conspicuous  element  of  the  pineal  region  in  am- 
phibia is  the  massive  and  vascular  paraphysis  which,  according 
to  certain  authorities,  reaches  its  highest  development  in  these 
forms.  It  has  all  the  characteristics  of  a  tubular  gland  with  a 
definite  sinusoidal  circulation  and  a  canal  which  connects  it  with 
the  ventricles  of  the  brain.  The  velum  trans versum  is  short 


32 


FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 


and  plexiform,  in  many  forms  attaining  a  marked  vascularity. 
The  next  structure  in  the  pineal  region  is  the  commissura  habenu- 
laris,  following  which  is  a  long  pars  intercalaris  anterior.  Then 
follows  the  epiphysis  or  the  proximal  portion  of  the  pineal  organ 
with  a  marked  pineal  recess.  There  can  be  little  doubt  that 
this  particular  form  in  which  the  pineal  organ  presents  itself 
is  the  actual  proximal  part  of  other  species.  Following  the 
epiphysis  is  a  thick  pars  intercalaris  posterior,  and  finally  the 
posterior  commissure. 


Npm 


M 


Fig.  4  Schematization  of  the  pineal  region  in  Amphibia,  according  to  Stud- 
nicka,  1905. 

Ls.,  lamina  terminalis;  P/.,  paraphysis;  Ds.,  dorsal  sac;  Ch.,  commissura  ha- 
benularis;  Po.,  pineal  organ;  Npir^,  nervus  pinealis;  Ep.,  proximal  portion  pineal 
organ;  Tp.,  tractus  pinealis;  Sch.,  pars  intercalaris  posterior;  Cp.,  commissura 
posterior;  M ..,  midbrain. 

7.  The  pineal  region  in  reptiia 

In  Prosaurians  and  Saurians,  as  in  Petromyzon  and  some 
teleosts,  both  the  pineal  and  parapineal  organs  make  their  appear- 
ance, but  the  order  which  they  hold  in  the  lower  forms  is  some- 
what reversed  here  since  the  parapineal  organ  gives  rise  to  an 
eye-like  structure  called  the  parietal  eye.  This  parietal  eye, 
however,  is  present  only  in  the  lower  reptiles.  The  pineal  organ, 


THE    PINEAL   BODY  33 

on  the  other  hand,  in  most  forms  presents  a  less  well-developed 
appearance,  and  in  many  instances  (in  Lensu  stricto)  an  epi- 
physis  cerebri  alone  may  be  observed.  The  parietal  eye,  earlier 
but  incorrectly  called  the  pineal  eye,  is  absent  in  many 
forms  even  among  the  lower  reptiles.  It  is  undoubtedly  the 
homologue  of  the  anterior  epiphyseal  organ  or  parapineal  organ 
of  teleosts  and  perhaps  the  parapineal  organ  of  Petromyzon. 
No  chapter  in  the  morphology  of  the  pineal  organ  is  more 
replete  with  interest  or  full  of  ..incentive  to  further  research  than 
that  dealing  with  the  remarkable  conditions  observed  in  this 
region  of  the  brain  in  reptilia.  From  the  observations  on  the 
Saurians  and  Prosaurians  have  come  far-reaching  theories  into 
the  phylogenesis  of  the  vertebrates  as  well  as  many  illuminating 
efforts  to  trace  the  evolution  of  this  phylum  by  means  of  the 
unpaired  parietal  eye  back  to  the  invertebrates.  Brandt40  in 
1829  was  first  to  mention  the  presence  of  the  epiphysis  in  the 
Saurian  brain.  Milne-Edwards107  and  Duges97  both  in  1829 
referred  to  certain  scales  in  the  head  of  Lacerta.  Neither  of 
these  authors  described  the  structures,  but  their  illustrations 
plainly  indicate  that  they  had  perceived  the  area  in  the  skull  in 
which  the  parietal  eye  comes  to  the  surface.  Cuvier77  and 
Tiedemann395  had  both  observed  the  organ  in  reptiles.  Ley  dig234 
in  1872  studied  the  embryo  of  Lacerta  and  Anguis,  giving  partic- 
ular attention  to  the  parietal  region  of  the  skull.  He  described 
a  peculiar  body  made  up  of  long,  epithelioid,  and  cylindrical 
cells.  These  cells  were  so  arranged  as  to  form  a  rim,  the  border 
of  which  comprises  cells  of  a  deep  black  pigment.  This  organ 
was  not,  as  one  might  think,  the  epiphysis,  for  this  latter  struc- 
ture lies  distinctly  above  the  organ  described  by  Leydig.  Ley- 
dig,  furthermore,  mentioned  a  parietal  foramen  and  a  spot  on 
the  skull  indicating  the  position  of  the  organ  which  lies  beneath 
it.  This  structure  Leydig  called  the  frontal  organ,  and  while  he 
strongly  suspected  that  it  was  possessed  of  sensory  function,  he 
did  not  commit  himself  to  such  a  theory  at  the  time  in  which  he 
wrote.  Strahl382  in  1884  thought  that  this  frontal  organ  of 
Leydig  had  certain  relations  to  the  epiphysis  and  seemed  able  to 
demonstrate  that  Leydig's  organ  was  nothing  more  than  a 


MEMOIR  NO. 


34 


FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 


detached  distal  portion  of  the  epiphysis,  the  homologue  of  the 
frontal  gland  in  amphibians.  The  idea  advanced  by  Strahl  was 
subsequently  confirmed  by  Hoffmann186  in  1886  and  again  by 
Beraneck21  in  1887.  But  it  is  to  deGraaf155  that  we  are  indebted 
for  the  first  demonstration  that  the  organ  of  Leydig  was  pro- 
vided with  a  lens  and  a  retina  and  was,  hence,  a  real  visual  organ. 
This  work  of  deGraaf  in  1886  was  almost  simultaneously  con- 


Fig.  5  Schematization  of  the  pineal  region  in  Sphenodon,  according  to  Stud- 
nicka,  1905. 

Ls.,  lamina  terminalis;  V.,  velum  transversum;  P/.,  paraphysis;  Ds.,  dorsal 
sac;  Ch.,  commissura habenularis;  Pa.,  parapineal  organ;  Npar.,  nervus  parapi- 
nealis;Po.,  pineal  organ;  Ep.,  proximal  portion  pineal  organ;  Tp.,  tractus  pinealis; 
Sch.,  pars  intercalaris  posterior;  Cp.,  commissura  posterior;  M.,  midbrain,  Np., 
accessory  parapineal  organ;  R.,  Recessus  pinealis. 

firmed  in  the  same  year  by  Spencer366  who  carried  on  a  large 
number  of  observations  upon  many  different  Saurian  forms, 
confirming  in  detail  the  proposition  advanced  by  deGraaf  that 
the  structure  described  by  Leydig  as  the  frontal  organ  contained 
not  only  a  lens,  but  a  definite  retina.  These  works  led  up  to 
the  later  investigations  on  the  parietal  eye  and  also  on  what  has 
been  called  the  third  eye  of  vertebrates. 


THE    PINEAL   BODY 


35 


The  parietal  eye  which  occurs  in  many  forms  of  Lacertilia  is, 
on  the  other  hand,  entirely  absent  in  Ophidians,  Chelonians,  and 
Crocodilians.  In  all  reptiles,  with  the  exception  of  Lacertilia, 
the  epiphyseal  complex  is  so  rudimentary  that  only  the  proximal 
portion  of  the  pineal  organ  remains.  Indeed,  in  Crocodilia  even 
this  is  said  to  be  absent. 


is. 


Fig.  6  Schematization  of  the  pineal  region  in  Ophidia,  according  to  Studnicka, 
1905. 

Ls.,  lamina  terminalis ;  P/.,  paraphysis;  V.,  velum  trans versum;  Ds.,  dorsal 
sac;  Ch.,  commissura  habenularis ;  Ep.,  proximal  portion  of  pineal  organ  (epiphy- 
sis);  Cp.,  posterior  commissure. 

Burckhardt45  in  1893  gave  the  first  description  of  the  pineal 
region  n  the  brain  of  Lacerta.  He  described  a  thin  and  flat 
lamina  supraneuroporica  above  which  arose,  to  a  considerable 
height,  a  simple  tubular  paraphysis.  In  adult  animals,  as  a 
rule,  this  structure  has  the  form  of  a  thin-walled  sac  lined  by 
cuboidal  ependymal  cells.  The  paraphysis  at  first  is  without 
vascularization,  but  later,  by  the  ingrowth  of  blood  vessels,  it 
becomes  highly  plexiform  in  character;  yet  in  no  instance  is  it 
comparable  to  the  vascularity  observed  in  Amphibians.  The 
distal  extremity  of  the  paraphysis  is  flexed  dorsally  and  often 


36  FREDERICK    TILNEY   AND    LUTHER   F.    WARREN 

comes  in  contact  with  the  ventrally  flexed  distal  extremity  of 
the  parietal  eye.  The  velum  transversum  is  well  developed  and 
is  plexiform  in  character,  being  highly  vascular  in  structure. 
Following  the  velum  transversum  is  a  dorsal  sac  usually,  how- 
ever, less  conspicuous  than  the  paraphysis  and  oftentimes  smaller 
than  that  organ.  The  commissura  habenularis  follows  and  is 
in  connection  with  two  symmetrical  ganglia  habenulae.  A  pars 
intercalaris  anterior  is  not  observed. 

The  epiphyseal  complex  has  a  different  arrangement  in  the 
several  different  classes  of  reptilia.  In  most  Lacertilia  the  part 
which  seems  to  be  the  homologue  of  the  parapineal  organ  has 
become  converted  into  a  definite  parietal  eye  with  lens,  retina, 
and  nerve  of  its  own.  The  pineal  organ,  on  the  other  hand,  is 
much  reduced  and  appears  but  a  remnant  of  the  homologue  of 
this  structure  in  some  of  the  lower  forms.  In  the  orders  of 
reptilia,  other  than  Lacertilia,  the  parapineal  organ  does  not 
develop  and  the  pineal  organ  itself  is  reduced  to  a  mere  rudiment, 
being  represented  wholly  by  the  development  of  its  proximal 
portion.  A  short  pars  intercalaris  posterior  follows  the  epi- 
physeal complex  while  a  relatively  large  posterior  commissure 
forms  the  caudalmost  structure  in  the  roof  of  the  interbrain. 

8.  The  pineal  region  in  aves 

In  birds,  only  the  proximal  portion  of  the  pineal  organ,  the 
part  usually  called  the  epiphysis  or  corpus  pineale,  develops. 
It  usually  appears  as  a  small  circumscribed  sac  connected  with 
the  roof  of  the  interbrain  or  else  it  has  a  definitely  glandular 
structure  with  acini  of  varying  size.  Mihalkovicz274  in  1874-77 
studied  the  epiphysis  in  Meleagris  gallopavo  and  in  this  bird 
called  attention  to  the  definite  follicular  and  glandular  char- 
acter of  the  tissue.  Mihalkovicz'  description  is  the  most  com- 
plete concerning  the  epiphysis  in  birds.  Galeotti140  in  1892 
added  some  details  to  Mihalkovicz'  description  of  this  struc- 
ture and  confirmed  the  opinion  that  it  was  glandular  in  its  nature. 
The  pineal  region  in  birds  is  compressed  cephalodorsad  because 
of  the  marked  development  of  the  hemispheres  and  the  cere- 


THE    PINEAL   BODY 


37 


bellum.  This  region  contains  in  more  or  less  rudimentary  form 
the  following  structures:  A  paraphysis,  a  very  simple  velum 
transversum,  a  small  and  compressed  dorsal  sac,  a  commissura 
habenularis,  an  epiphysis,  undoubtedly  the  homologue  of  the 
proximal  portion  of  the  pineal  organ  with  a  definite  pineal  recess 
and  a  pineal  peduncle,  a  pars  intercalaris  posterior  of  varying 
size  depending  upon  the  species,  and  a  fairly  well-marked  pos- 
terior commissure.  The  relation  of  the  epiphysis  to  the  brain 
roof  in  birds  is  different  from  that  encountered  in  any  of  the 


Ls-       ^      «  , 

Ch      C'p  - 

tL 

Fig.  7  Schematization  of  the  pineal  region  in  Aves,  according  to  Studnicka, 
1905. 

Ls.,  lamina  terminalis;  P/.,  paraphysis;  Ds.,  dorsal  sac;  Ch.,  commissura 
habenularis;  Ep.,  proximal  portion  of  pineal  organ  (epiphysis);  Cp.,  posterior 
commissure;  M.,  midbrain. 

lower  forms  in  that  here  the  axis  of  the  organ  is  at  right  angles 
to  the  roof,  whereas,  lower  in  the  scale  the  tendency  has  been 
for  the  body  to  show  a  definite  anterior  or  ventral  flexion. 

9.  The  pineal  region  in  mammals 

This  region  is  made  up  as  follows  in  the  mammal:  Following  a 
thin  lamina  supraneuroporica  there  occurs,  according  to  Fran- 
cotte129  in  1894  in  the  early  stages  of  development  in  the  human 
embryo,  a  short  tubular  process  which  he  terms  the  paraphysis. 


38  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

d'Erchia  ('96) 109  found  this  structure  only  as  a  simple  fold  in 
the  embryo,  while  recently  Warren  ('17)417  has  identified  a  small 
but  solid  protuberance  at  the  anterior  extremity  of  the  inter- 
brain  roof-plate  in  the  human  embryo  which  he  believes  is  the 
anlage  of  the  paraphysis.  This,  however,  soon  disappears,  leav- 
ing no  trace  of  its  presence,  although  there  develops  in  the 
neighborhood  of  its  origin  certain  prolongations  which  Warren 
has  described  as  the  diencephalic  prolongations.  In  the  adult 
brain  of  other  mammalian  forms  no  paraphysis  has  been  ob- 
served. The  velum  transversum,  if  present  at  all,  has  been 
observed  in  the  early  embryonic  period  only  and  then  as  a  simple 
fold.  This  statement  is  based  on  the  observations  of  d'Erchia. 
The  dorsal  sac,  because  of  the  much-altered  condition  in  the 
mammalian  brain  due  to  the  development  of  the  corpus  callosum, 
has  become  much  flattened  and  reduced  to  the  level  of  the  general 
plain  of  the  roof-plate.  It  has  undergone  further  change  in  the 
fact  that  it  has  acquired  a  rich  vascularization  and  become 
definitely  plexiform,  giving  rise  to  the  tela  chorioidea  superior 
of  human  anatomy.  The  caudalmost  portion  of  the  dorsal  sac 
immediately  in  front  of  the  epiphysis  is  elevated  and  pushed 
back  over  the  dorsal  surface  of  the  pineal  body  in  such  a  way  as 
to  form  a  thin,  roofed  sac  whose  ventral  wall  lies  upon  the  dorsal 
surface  of  the  epiphysis.  This  is  the  recessus  suprapinealis 
described  by  Reicher^326  in  1859.  A  commissura  habenularis  is 
the  next  element  in  the  roof-plate,  and  this  is  situated  in  relation 
with  the  peduncle  of  the  epiphysis.  The  epiphysis  in  mammals 
undoubtedly  represents  the  proximal  portion  of  the  pineal  organ. 
The  epiphysis  itself  is  a  solid,  more  or  less  conical  shaped  body 
connected  with  the  roof  of  the  brain  by  one  or  more  sets  of 
so-called  peduncles.  As  a  result  of  the  development  of  the 
corpus  callosum,  the  epiphysis  has  gradually  been  brought  to 
assume  a  position  which  brings  it  into  relation  with  the  superior 
colliculi  of  the  midbrain.  Situated  between  the  epiphyseal 
peduncles  there  is  a  small  pineal  recessus.  The  entire  epiphysis 
is  located  in  a  position  much  removed  from  the  inner  surface  of 
the  skull. 


THE    PINEAL   BODY 


39 


M 


Fig.  8  Schematization  of  the  pineal  region  in  Mammals,  according  to  Stud- 
nicka,  1905. 

Ds.,  dorsal  sac;  Ch.,  commissura  habenularis;  R.,  recessus  pinealis;  Ep.,  proxi- 
mal portion  of  the  pineal  organ  (epiphysis);  Cp.,  commissura  posterior;  M., 
midbrain. 

In  the  light  of  the  phyletic  review  just  given  concerning  the 
structures  constituting  the  pineal  region,  it  becomes  clear  that 
any  satisfactory  consideration  of  the  epiphyseal  complex  must 
take  into  account  the  characters  of  the  parapineal  organ  as 
well  as  those  of  the  pineal  organ.  It  seems  advantageous  to 
discuss  the  comparative  embryology  of  these  two  parts  and 
then  to  consider  the  phyletic  characteristics  of  each  of  them 
separately.  In  this  way  the  modifications  of  each  organ  may  be 
followed  consecutively  from  one  order  to  the  next. 

5.  THE  COMPARATIVE  EMBRYOLOGY  OF  THE  EPIPHYSEAL  COMPLEX 
1.  The  development  of  the  epiphyseal  complex  in  cyclostomes 

According  to  Studnicka  (;93)384  and  other  observers,  a  small 
evagination  in  the  caudal  portion  of  the  roof-plate  of  the  inter- 
brain  makes  its  appearance  as  a  simple  and  single  protrusion 
from  the  roof.  This  is  the  pineal  organ.  There  can  be  no 
question  but  that  it  develops  first  of  the  two  elements  in  the 
epiphyseal  complex  in  these  forms.  The  anlage  of  the  pineal 
organ  increases  greatly  in  size  so  as  to  present  an  end-sac  or 


40 


FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 


end-vesicle,  a  stalk  and  a  proximal  portion  connecting  it  with  a 
ventricle  of  the  brain.  At  first,  the  end-vesicle  contains  a  cavity 
which  gradually  decreases  in  size  so  that  the  lumen  becomes 
little  more  than  a  cleft  or  entirely  disappears.  The  stalk  also 
contains  a  large  canal  which  is  gradually  reduced  in  size.  The 
ventral  wall  of  the  end-sac  becomes  converted  into  a  structure 
resembling  the  retina,  in  which  many  nerve  fibers  are  to  be 
observed.  In  the  dorsal  wall  of  the  sac  nerve  fibers  running 
from  the  end-vesicle  soon  make  their  appearance.  These  fibers 
come  into  relation  with  the  posterior  commissure  and  constitute 
what  is  known  as  the  nervus  pinealis.  The  proximal  portion  is 
represented  by  a  very  short,  dilated  structure  which  contains 
the  recessus  pinealis. 


Fig.  9  Anlage  of  the  epiphyseal  conplex  in  an  embryo  of  Petromyzon,  accord- 
ing to  Kupffer,  1904. 

Ls.,  lamina  terminalis;  Pp.,  paraphysis;  Ch.,  commissura  habenularis;  Po., 
pineal  organ;  Cp.,  commissura  posterior. 

At  a  considerably  later  embryonic  period  the  anlage  of  Stud- 
nicka's  parapineal  organ  first  makes  its  appearance.  It  develops 
entirely  independent  of  the  anlage  of  the  pineal  organ.  The 
evagination  which  first  makes  its  appearance  as  the  parapineal 
anlage  shortly  becomes  greatly  elongated  to  form  a  tubular 
prolongation  from  the  roof  of  the  brain.  The  terminal  portion  of 
this  tubular  evagination  becomes  dilated  to  form,  as  in  the  case  of 
the  pineal  organ,  an  end- vesicle,  while  a  slender  stalk  connects  the 
latter  with  the  brain  roof.  The  ventral  wall  of  the  end-sac  of 
the  parapineal  organ,  as  in  the  case  of  the  pineal  organ,  develops 


THE    PINEAL   BODY  41 

a  pigmented  structure  and  in  it  appears  a  number  of  nerve  fibers. 
In  the  later  embryonic  stages  the  stalk  connecting  the  end- 
vesicle  of  the  parapineal  organ  with  the  brain  attenuates,  loses 
its  lumen,  and  shows  the  presence  in  it  of  numerous  nerve  fibers 
which  may  be  traced  to  the  commissura  habenularis.  The  rapid 
elongation  of  the  stalk  in  the  parapineal /and  pineal  organs  as 
development  advances  causes  these  structures  to  be  moved 
further  away  from  the  roof-plate  and  near  the  under  surface  of 
the  skull.  The  general  direction  of  this  growth  is  cephalodorsad. 
Gaskell145  showed  in  Ammoccetes  a  right  and  left  pineal  eye. 
It  is  his  opinion  that  the  pineal  and  parapineal  organs  represent 
a  paired  set  of  eyes.  Their  relation  to  each  other,  in  which  the 
parapineal  organ  occupies  the  more  cephalic  position,  was  deter- 
mined, according  to  Gaskell,  by  the  exigencies  of  development. 
In  reality,  however,  he  believes  that  the  ancestors  of  vertebrates 
must  have  possessed  a  pair  of  median  eyes. 

Dendy86  also  observed  in  cyclostomes  a  double  evagination 
from  the  roof-plate  giving  rise  to  the  epiphyseal  complex.  It  is 
his  opinion  that  the  right  evagination  produces  the  parietal  eye 
while  the  left  becomes  the  parapineal  organ,  and  Dendy,  like 
Gaskell,  maintains  that  the  ancestors  of  the  vertebrates  must 
have  been  possessed  of  a  pair  of  parietal  eyes  which  may  have 
been  serially  homologous  with  the  ordinary  vertebrate  eyes. 
Scott  ('81)349  and  Dohrn  (75) 95  both  showed  that  the  epiphyseal 
complex  developed  as  evaginations  from  the  roof  of  the  in- 
terbrain.  These  observations  were  essentially  confirmed  by 
Shipley  ('87),354  Owsiannikow  ('88),295  Studnicka  (793),384  and 
Kupffer  ('94). 224 

2.  The  development  of  the  epiphyseal  complex  in  selachians 

Balfour10  in  1878,  in  Acanthias,  d'Erchia109  in  1896,  in  Pris- 
tiurus,  and  Minot277  in  1902,  also  in  Pristiurus,  investigated  the 
development  of  the  epiphyseal  complex.  According  to  all  of 
these  authors,  a  single  evagination .  arises  in  the  roof -plate  im- 
mediately in  front  of  what  is  later  to  be  the  posterior  commissure. 
This  evagination  gives  rise  to  the  pineal  organ  inasmuch  as  the 
parapineal  organ  does  not  appear  in  selachians.  From  its 


42  FREDERICK   TELNET   AND    LUTHER   F.    WARREN 

inception  this  evagination  is  a  small,  cordiform  enlargement 
which  rests  at  first  directly  upon  the  ectoderm  of  the  upper 
surface  of  the  head.  The  gradual  lengthening  of  the  tubular 
pineal  organ,  which  is  similar  to  what  occurs  in  Petromyzon,  is 
in  the  main  due  to  the  fact  that  a  very  large  amount  of  mesen- 
chyme  makes  its  appearance  between  the  roof  of  the  brain  and 
the  under  surface  of  the  skull.  In  this  way  the  end-vesicle  of 
the  pineal  organ  maintains  its  relative  position  to  the  ectoderm 
and  thus  always  remains  near  the  surface  of  the  skin.  In  many 
instances  the  end-vesicle  comes  to  lie  in  a  large  foramen  of  the 
skull,  that  is,  the  parietal  foramen  which  makes  its  appearance 
at  a  later  stage  of  development. 

Considering  the  embryological  development  of  the  pineal 
region  in  selachians,  Locy244  holds  that  two  pairs  of  accessory 
optic  vesicles  are  preserved  in  the  cephalic  plate  of  Elasmo- 
branchs,  his  particular  reference  being  to  Squalus  acanthias. 
These  accessory  optic  vesicles  together  with  the  primary  optic 
vesicles  give  rise  to  two  pairs  of  rudimentary  eyes.  The  epi- 
physis  is,  therefore,  of  double  origin,  forming  a  united  pair  of 
accessory  optic  vesicles,  and  since  the  latter  are  homologous 
with  the  lateral  eyes,  the  epiphysis  itself  must  be  homologous 
with  these  eyes  also.  His  contention  that  the  pineal  outgrowths 
arise  from  two  pairs  of  vesicles  that  are  homologous  with  those 
giving  origin  to  the  lateral  eyes  has  not  been  altogether  sustained 
by  other  observers.  Locy  is  also  of  the  opinion  that  it  is  highly 
probable  that  the  enlarged  distal  end  of  the  epiphysis  in  Squalus 
is  homologous  with  the  pineal  eye  in  those  forms  in  which  it  is 
differentiated.  Goette152  in  1875  expressed  the  opinion  that  the 
epiphysis  in  selachians  was  a  product  of  differentiation  at  the 
point  of  union  between  the  brain  and  the  epidermis.  He  com- 
pares the  pineal  organ  to  the  pore  which  persists  for  a  long  time 
in  the  embryo  of  Amphioxus  and  leads  into  the  encephalic  cavi- 
ties. Ehlers108  in  1878  confirmed  the  findings  of  Balfour  in 
Raia  clavata  and  Acanthias  vulgaris.  An  interesting  observa- 
tion in  this  connection  is  the  finding  by  Cattie60  of  the  pineal 
organ  in  Torpedo  marmorata.  Cattie  observed  the  organ  in  the 
embryonic  state  in  this  form.  The  importance  of  this  observa- 


THE    PINEAL    BODY 


tion  lies  in  the  fact  that  Studnicka391  says  that  the  organ  is  absent 
in  Torpedo  marmorata  and  d'Erchia109  says  that  in  Torpedo 
ocellata  there  is  no  pineal  organ. 


Fig.  10  The  epiphyseal  complex  in  an  86  mm.  embryo  of  Acanthias  vulgaris, 
according  to  Minot,  1901. 

Hm.,  hemisphere;  Pf.,  paraphysis,  V.,  velum  transversum;  Ds.,  dorsal  sac: 
Ch.,  commissura  habenularis;  R.,  recessus  pinealis;  Po.,  pineal  organ;  Cp.,com- 
missura  posterior;  M.,  midbrain. 

One  of  the  authors,  Tilney  ('15),396  studying  the  interbrain  in 
Mustelus  laevis,  illustrated  the  development  of  the  pineal  organ 
in  reconstruction  models  through  a  number  of  stages.  The 
anlage  of  the  epiphyseal  complex  in  Mustelus  makes  its  first 
appearance  in  the  9  mm.  embryo  as  a  single  evagination  from  the 
roof-plate.  It  is  a  prominent  element  in  this  region  for  some 


44  FKEDERICK   TILNEY   AND    LUTHER   F.    WARREN 

time  before  the  appearance  of  the  paraphysis.  In  the  embryo 
of  an  •!!  mm.  Mustelus  the  evagination  appears  rising  well 
above  the  general  plane  of  the  roof. 

It  is  bounded  by  a  thin  cephalic  and  a  thicker  caudal  wall. 
A  recess  of  considerable  depth  extends  into  it;  it  retains  com- 


44 


29 


Fig.  11  Mesial  view  of  forebrain  reconstruction  of  11  mm.  Mustelus  embryo. 
X  100.  The  unshaded  area  shows  the  cut  surfaces  of  the  reconstruction.  Ac- 
cording to  Tilney,  1915. 

4,  chiasm;  7,  epiphysis;  18,  infundibular  evagination;  24,  midbrain;  25,  mam- 
millary  region;  29,  optic  evagination;  36,  post-infundibular  evagination;  44,  tel- 
encephalon;  45,  tuberculum  postero-superius;  46,  tubercle  of  the  floor  of  Schulte. 

munication  with  the  third  ventricle.  The  inception  of  the  velum 
transversum  may  be  discerned,  but  no  paraphysis  is  present. 
The  changes  observed  in  passing  from  the  11  mm.  to  the  20  mm. 
embryo  consist  in  the  now  definite  appearance  of  the  velum 
transversum  and  the  elongation  of  the  pineal  organ. 


THE    PINEAL   BODY 
24 


45 


42 


3332 


Fig.  12  Mesial  view  of  forebrain  reconstruction  of  20  mm.  Mustelus.  X  75. 
The  unshaded  area  shows  the  cut  surfaces  of  the  reconstruction.  According  to 
Tilney,  1915. 

2,  chiasmatic  process;  3,  cerebellum;  4,  chiasm;  7,  epiphysis;  18,  infundibular 
evagination;  24,  midbrain;  25,  mammillary  region;  32,  post-chiasmatic  eminence; 
33,  post-chiasmatic  recess;  36,  post-infundibular  eminence;  41,  supra-optic  crest; 
42,  supra-optic  recess;  44,  telencephalon;  45,  tuberculum  postero-superius ;  46, 
tubercle  of  the  floor  of  Schulte;  47,  velum  transversum. 

In  the  latter  there  is  a  slight  tendency  for  the  evagination  to 
become  expanded  as  if  to  form  an  end-vesicle.  It  is,  therefore, 
possible  at  this  time  to  recognize  a  stalk  and  an  end-sac. 
Neither  in  this  stage  nor  in  any  subsequent  period  of  develop- 
ment is  there  evidence  of  a  parapineal  organ.  The  paraphysis 


46 


FREDERICK    TILNEY    AND    LUTHER    F,    WARREN 


has  not  yet  made  its  appearance.  In  the  50  mm.  embryo,  how- 
ever, the  paraphyseal  anlage  is  present  and  the  pineal  organ 
has  become  still  further  elongated. 

The  tendency  toward  expansion  of  the  dista1  extremity  is  not 
as  marked  as  in  the  20  mm.  embryo.  The  pineal  organ  still 
contains  a  lumen  throughout  its  entire  extent.  The  expansion 
of  the  pineal  organ  to  form  an  end-sac  is  again  pronounced  at 
the  stage  of  70  mm. 

44 


39 


32 


13 


Fig.  13  Mesial  view  of  forebrain  reconstruction  of  50  mm.  Mustelus.  X  50. 
The  unshaded  area  shows  the  cut  surfaces  of  the  reconstruction.  According  to 
Tilney,  1915. 

2,  chiasmatic  process;  3,  cerebellum;  4,  chiasm;  7,  epiphysis;  13,  infundibular 
process;  24,  midbrain;  25,  mammillary  region;  32,  post-chiasmatic  eminence 
(lobus-inf erior) ;  33,  post-chiasmatic  recess  (recess  of  inferior  lobe);  36,  post- 
infundibular  evagination;  39,  paraphysis;  40,  recess  of  infundibular  process;  41, 
supra-optic  crest ;  42,  supra-optic  recess ;  44,  telencephalon ;  47,  velum  transversum . 


THE    PINEAL   BODY 


47 


The  sac  is  hollow  and  in  communication  with  the  ventricle  by 
means  of  a  slender,  hollow  stalk.  A  proximal  portion  may  now 
be  distinguished  so  that  all  three  elements  of  the  pineal  organ  are 
present.  The  habenular  ganglion  is  recognizable  at  this  stage 
as  a  marked  thickening  in  the  roof-plate  cephalad  of  the  pineal 
organ.  The  paraphysis  and  velum  have  increased  in  promi- 


24 


42 


Fig.  14  Mesial  view  of  forebrain  reconstruction  of  70  mm.  Mustelus.  X  50. 
The  unshaded  area  shows  the  cut  surfaces  of  the  reconstruction.  According  to 
Tilney,  1915 

2,  chiasmatic  process;  3,  cerebellum;  4,  chiasm;  7,  epiphysis;  18,  infundibular 
evagination;  24,  midbrain;  26,  mammillary  recess;  27,  mammillary  body  (poste- 
rior lobe) ;  32,  post-chiasmatic  eminence  (inferior  lobe) ;  33,  post-chiasmatic 
recess  (recess  of  inferior  lobe) :  35,  post-infundibular  recess;  36,  post-infundibular 
eminence;  39.  paraphysis;  40,  recess  of  infundibular  process;  41,  supra-optic  crest; 
42,  supra-optic  recess;  44,  telencephalon;  47,  velum  transversum. 

nence.  The  brains  of  the  100  mm.  and  300  mm.  Mustelus 
approximate  the  adult  conditions  shown  in  figures  15,  16  and  17. 
Here,  with  one  exception,  i.e.,  the  parapineal  organ,  all  of  the 
elements  in  the  pineal  region  may  be  identified,  including  the 
two  parts  of  the  paraphyseal  arch,  the  velum  transversum,  a 
short  dorsal  sac,  a  massive  habenular  commissure  and  habenular 


48 


FREDERICK    TILNEY   AND    LUTHER   F.    WARREN 


ganglion,  a  pineal  organ  consisting  of  an  end-vesicle,  stalk  and 
proximal  portion,  and  finally  the  posterior  commissure. 


39 


Fig.  15  Mesial  view  of  brain  reconstruction  of  100  mm.  Mustelus.  X  25. 
The  unshaded  area  shows  the  cut  surfaces  of  the  reconstruction.  According 
to  Tilney,  1915. 

2,  chiasmatic  process;  3,  cerebellum;  4,  chiasm;  7,  epiphysis;  13,  infundibular 
process;  14,  infundibular  process,  saccular  surface;  15,  infundibular  process,  pitui- 
tary surface;  20,  lamina  terminalis;  24,  midbrain;  27,  mammillary  body  (post- 
erior lobe) ;  32,  post-chiasmatic  eminence  (lobus  inferior) ;  33,  post-chiasmatic 
recess  (recess  of  inferior  lobe);  36,  post-infundibular  evagination;  39,  paraphysis; 
40,  recess  of  infundibular  process;  41,  supra-optic  crest;  42,  supra-optic  recess; 
44,  telencephalon;  47,  velum  transversum. 

3.  The  development  of  the  epiphyseal  complex  in  ganoids 

Kupffer223 1893  gave  the  first  detailed  description  of  the  develop- 
ment of  the  epiphyseal  complex  in  Acipenser.  The  anlage  of  the 
organ  he  describes  as  a  small  single  evagination  which  later 
becomes  a  stalk  with  an  end-vesicle.  Kupffer  could  find 
nothing  of  the  anterior  or  parapineal  organ.  Owsiannikow 
(J88)295  gave  a  description  according  to  which  in  the  three-  or 
four- weeks  old  embryo  of  Acipenser  just  in  front  of  the  pineal 
organ  there  appears  a  small,  round  or  cordiform  structure.. 
Hill180  in  1894  described  a  small  rudiment  of  the  anterior  or 
parapineal  organ  in  Amia  calva.  In  the  10  mm.  embryo  this 
body  was  ovoid  in  form  and  situated  immediately  in  front  and 


THE    PINEAL  BODY  49 

to  the  left  of  the  pineal  organ.  It  was  connected  with  the  roof- 
plate  by  means  of  a  thin  stalk.  In  the  13  mm.  embryo  this 
organ  has  come  to  lie  above  the  commissura  habenularis  and 
still  later  it  is  consolidated  into  a  mass  of  cells  lying  to  the  left 
beneath  the  now  markedly  developed  and  ventrally  flexed 
pineal  organ.  Eycleshymer  and  Davis113  in  1897  confirmed  the 
observation  of  Hill  and  noted  that  the  anterior  or  parapineal 


44 


15 10 

32  33 

Fig.  16  Mesial  view  of  brain  reconstruction  of  300  mm.  Mustelus.  X  25. 
The  unshaded  area  shows  the  cut  surfaces  of  the  reconstruction.  According  to 
Tilney,  1915. 

2,  chiasmatic  process;  3,  cerebellum;  4,  chiasm;  7,  epiphysis;  10,  hypophyseal 
recess;  13,  infundibular  process;  14,  infundibular  process,  saccular  surface;  15, 
infundibular  process,  pituitary  surface;  24,  midbrain;  27,  mammillary  body  (pos- 
terior lobe);  32,  post-chiasmatic  eminence  (inferior  lobe);  33,  post-chiasmatic 
recess  (recess  of  inferior  lobe);  36,  post-infundibular  evagination;  39,  paraphysis; 
40,  recess  of  the  infundibular  process;  41,  supra-optic  crest;  42,  supra-optic  re- 
cess; 44,  telencephalon;  47.  velum  transversum. 

organ  possessed  a  lumen  late  in  the  course  of  development. 
Both  the  anterior  and  posterior  pineal  organs  in  the  embryonic 
stages  have  nerve  fibers  which  connect  them  with  the  habenular 
commissure.  The  earlier  works  upon  this  region  in  ganoids  were 
done  by  Salensky341  in  1881  and  Balfour  and  Parker12  in  1882 
(%  18). 

MEMOIR  NO.  9 


50  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

4.  The  development  of  the  epiphyseal  complex  in  teleosts 

Rabl-Rtickhard318  in  1882  gave  the  first  explanation  of  the 
development  of  the  epiphyseal  complex  in  teleosts.  Hoffmann185 
in  1884  also  described  the  ontogenesis  of  the  pineal  organ  in 


14 


33 


21 


Fig.  17  Mesial  view  of  brain  reconstruction  in  adult  Mustelus  laevis.  X  25. 
The  unshaded  area  shows  the  cut  surfaces  of  the  reconstruction.  According  to 
Tilney,  1915. 

2,  chiasmatic  process;  3,  cerebellum;  4,  chiasm;  6,  diverticular  sacci  vasculosi; 
7,  epiphysis;  10,  hypophyseal  recess;  12,  infundibular  canal;  14,  infundibular  proc- 
ess, saccular  surface;  15,  infundibular  process,  pituitary  surface;  20,  lamina  ter- 
minalis;  21,  median  chiasmatic  groove;  24,  midbrain;  26,  mammillary  recess  (re- 
cess of  posterior  lobe) ;  27,  mammillary  body  (posterior  lobe) ;  32,  post-chiasmatic 
eminence  (inferior  lobe) ;  33,  post-chiasmatic  recess  (recess  of  inferior  lobe) ;  34, 
post-infundibular  eminence;  35,  post-infundibular  recess;  39,  paraphysis;  42, 
supra-optic  recess;  44,  telencephalon;  47,  velum  transversum. 

teleosts.  Both  authors  employed  the  same  forms,  namely, 
Salmo  fario  and  Salmo  solar.  According  to  their  descriptions, 
the  anlage  begins  as  a  small  evagination  which  gradually  elon- 
gates and  grows  more  and  more  narrow.  It  has  produced  a 
proximal  portion,  a  stalk  and  an  end- vesicle  which  lie  just 
beneath  the  inner  surface  of  the  skull  in  the  frontal  region. 


THE    PINEAL    BODY 


51 


Still  later  many  small  diverticula  develop  in  the  walls  of  the 
end-vesicle  which  become  unusually  large.  A  feature  of  the 
description  of  the  development  given  by  these  authors  is  the 
absence  of  any  anterior  or  parapineal  element  in  the  epiphyseal 
complex,  for  this  organ,  according  to  their  observations,  does 


M 


Cp  R  Ch     Ds      V         Pf 


Rn 


Fig.  18  The  epiphyseal  complex  in  a  four  months  old  embryo  of  Acipenser 
sturio,  according  to  Kupffer,  1893. 

Ls.,  lamina  terminalis;  Pf.,  paraphysis;  V.,  velum  trans versum;  Ds.,  dorsal 
sac;  Ch.,  commissura  habenularis;  R.,  recessus  pinealis  and  pineal  organ;  Cp., 
commissura  posterior;  M.,  midbrain. 

not  even  make  its  appearance  in  anlage.  Holt  ('91) 189  described 
the  development  of  the  epiphyseal  complex  in  Clupea  harengus. 
In  this  form  the  organ  began  as  a  solid  sprout  and  later  devel- 
oped a  lumen.  The  walls  of  the  end- vesicle  were  eventually 
thrown  into  a  number  of  diverticula.  Mclntosh  and  Prince254 
in  1891  confirmed  the  findings  of  Hoffmann  and  Rabl-Ruckhard. 
Hill's179  observation  in  1891  is  of  unusual  importance,  for  this 
observer,  working  upon  Coregonus  albus  and  later180  in  1894  on 
Salmo  catostomus  teres,  Stizosthetium  vitreum,  and  Liponus 
callidus,  found  what  he  took  to  be  the  anlage  of  the  anterior  or 
parapineal  element  just  as  he  had  found  this  element  in  Amia 


52  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

calva.  In  the  embryo  of  Salmo  fontinalis ,  Hill180  found  the 
anlage  of  the  epiphyseal  complex  to  be  a  double  evagination 
which  communicated  with  the  third  ventricle  by  means  of  a 
common  canal.  Of  the  two  sacs  thus  formed  the  posterior  was 
much  the  larger.  This,  the  anlage  of  the  pineal  organ,  was 
situated  immediately  in  front  of  the  posterior  commissure  and 
in  the  mid-line,  while  the  anterior  evagination  was  close  to  the 
left  as  if  both  sacs  were  related  to  the  roof-plate  by  a  common 
stalk  and  later  the  anterior  one  was  detached  from  the  connec- 
tion. Hill  concluded  that  there  are  two  epiphyseal  outgrowths 
from  the  roof  in  teleosts  of  which  the  more  anterior  vesicle,  both 
in  teleosts  and  in  Amia,  is  homologous  with  the  parietal  eye  of 


Po 


Pp 


Fig.  19  Anlage  of  the  epiphyseal  complex  in  a  37.-days  old  embryo  of  Salmo 
fontinalis,  according  to  Hill,  1894. 

Pp.,  parapineal  organ;  Po.,  pineal  organ. 

Lacertilia.  He  thinks  it  probable  that  the  two  vesicles  in  their 
primitive  position  were  side  by  side  and  believes  it  likely  that 
the  anterior  vesicle  is  the  homologue  of  the  parapineal  organ  in 
Petromyzon.  Hill  also  found  this  condition  in  embryos  as  well 
as  in  a  two-year-old  salmon. 

Dendy86  maintained  that  the  double  evagination  in  the  epi- 
physeal anlage  occurs  in  Amia  as  well  as  leleosts.  Of  these  two 
vesicles  the  right  gives  rise  to  the  epiphysis  while  the  left  sepa- 
rates from  the  brain  and  degenerates.  Cattie,60  examining  the 
adult  condition  in  plagiostomes,  ganoids,  and  teleosts,  came  to  a 
conclusion  similar  to  the  hypotheses  of  Goette152  and  Van  Wijhe407 
that  the  pineal  body  was  derived  as  the  final  product  of  closure 
at  the  anterior  neuropore  where  the  ectoderm  of  the  epidermis 


THE    PINEAL   BODY  53 

and  of  the  nerve  tube  remained  longest  in  continuity.  Van 
Wijhe407  in  1884  expressed  the  belief  that  the  epiphysis  in  teleosts 
was  a  remnant  of  the  anterior  neuropore,  but  later  he  gave  up 
this  idea.  Rabl-Riickhard318  in  1882,  studying  the  epiphysis  in 
embryos  of  bony  fish,  summarized  the  process  of  development 
from  the  comparative  standpoint  in  the  following  words: 

Allein  wahrend  diese  unter  Mitwirkung  des  sich  zur  Linse  einstul- 
penden  Ectoderms  und  des  Mesoderms  complicirte  Veranderungen  ein- 
gehen,  die  schliesslich  zur  Entwickelung  des  hochst  entwickelten  Sin- 
nesorganes,  des  Auges,  fiihren,  sehen  wier  an  der  Zirbeldriise  trotz  der 
giinstigen  Lage  ihres  distalen  Endes  dicht  unter  dem  Ectoderm  nichts 
dergleichen.  Mann  denke  sich  eine  ahnliche  Wucherung  und  ihre  Folgen, 
wie  an  dem  die  Augenblasen  bedeckenden  Ectoderm,  das  Auftreten  von 
Pigment  im  sich  betheiligenden  Mesoderm,  und  nichts  steht  der  Vor- 
stellung  im  Wege,  dass  sich  aus  der  Zirbel  ein  dem  Auge  dhnliches,  un- 
paares  Sinnesorgan  entwickelt.  Interessant  ist,  dass  diese  Gegend  in 
einem  bestimmten  Embryonal-stadium  bei  Reptilien  (Lacerta  Anguis) 
eine  ahnliche  Entwickelung  wenigstens  andeutungsweise  zeigt,  und  dass 
hier  am  Scheitelbeine  des  fertigen  Thieres  sich  ein  Kreisrundes  Loch 
befindet.  Bekanntlich  hat  schon  Ley  dig  diesen  Befund  eingehend 
erortert  und  die  Vermuthung  ausgesprochen,  dass  es  sich  vielleicht  um 
ein  "Organ  des  6  Shines"  handelt. 

And  again  in  1886: 

Das.  Schadeldach  der  riesigen  fossilen  Enaliosaurier  des  Lais  des  Ich- 
thyosaurus und  Plesiosaurus  besitzt  ein  unpaares  Loch,  welches  seiner 
Lage  nach  mit  dem  Loch  in  Scheitelbein  der  Saurier  ubereinzustimmen 
scheint.  Vielleicht  lag  auch  hier  das  viel  entwickeltere  Zirbelorgan 
mit  seinem  distalen  Endtheil  zu  Tage,  und  man  konnte  sich  vorstellen 
das  seine  Leistung  nicht  sowohl  die  eines  Sehorgan  als  die  eines  Organs 
des  Warmesinnes  war,  dazu  bestimmt,  seine  Trager  vor  der  zu  inten- 
siven  Einwirkung  der  trophischen  Sonnenstrahlen  zu  warnen,  wenn  sie 
in  trager  Ruh,  nach  Art  ihrer  noch  lebenden  Vettern  der  Crocodile, 
sich  am  Strande  und  auf  den  Sandbanken  der  Laisse  sonnten. 

5.  The  development  of  the  epiphyseal  complex  in  amphibia 

In  Urodela,  deGraaf  ('86) 155  found  that  the  embryo  of  Triton 
had  the  anlage  of  its  epiphyseal  complex  in  a  simple  and  single 
saccular  evagination  from  the  roof  of  the  interbrain.  These 
observations  were  confirmed  upion  Amblyswma  embryos  by 
Orr286  in  1899,  by  His183  in  1892  and  by  Eycleshymer112  in  1892. 
Beraneck24  in  1893,  working  upon  Salamandra  embryos,  observed 


54  FREDERICK    TILNEY   AND    LUTHER    F.    WARREN 

the  anlage  of  the  epiphyseal  complex  to  be  a  hollow  sac  which 
later  became  saccular  and  cylindrical,  containing  throughout  its 
entire  extent  a  lumen  which  still  opened  into  the  third  ventricle. 
In  this  form  it  was  possible  to  identify  an  end- vesicle,  a  stalk,  and 
a  proximal  portion.  These  conditions  were  obtained  at  a  period 
of  12  mm.  embryo,  but  at  the  stage  of  the  18-mm.  embryo  the 
lumen  in  the  stalk  was  obliterated.  In  this  manner  the  stalk  of 
the  pineal  organ  became  gradually  reduced  in  size  until  finally 
it  presented  itself  as  a  mere  strand  connecting  an  almost  com- 
pletely isolated  end-vesicle  lying  beneath  the  skull  with  a  well- 
marked  proximal  portion  in  communication  with  the  third 
ventricle.  In  Salamandra  the  paraphysis  develops  very  early 
and  assumes  extensive  proportions  resembling  the  chorioid 
plexus.  The  embryological  conditions  in  Anura  are,  according 
to  most  descriptions,  quite  similar  to  those  in  Urodela.  Goette152 
in  1873-75  observed  in  the  anlage  of  the  pineal  organ  the  remains 
of  the  anterior  neuropore.  This  error,  as  has  already  been 
stated,  was  pointed  out  by  Hoffmann186  in  1886  and  Heckscher1690 
in  1890.  In  Rana,  Beraneck24  described  the  first  appearance  of 
the  anlage  of  the  epiphyseal  complex  as  a  small,  ellipsoid  evagi- 
nation  which  later  becomes  cylindrical.  This  evagination  con- 
tains a  small  lumen.  Elongation  gradually  occurs  so  that  an 
end- vesicle,  a  stalk,  and  a  proximal  portion  are  formed.  In  the 
later  stages  of  development  the  stalk  undergoes  attenuation 
until  it  is  reduced  to  a  mere  strand  containing,  it  is  thought, 
some  nerve  fibers.  This  leaves  the  end-vesicle  situated  at  a 
point  remote  from  the  brain  beneath  the  skull,  while  the  proximal 
portion  is  a  large  and  somewhat  spacious  evagination  still  main- 
taining a  wide  connection  with  the  third  ventricle.  The  nearly 
isolated  end- vesicle  Beraneck  calls  the  corpus  epitheliale.  This 
body  lies  beneath  the  skin  over  the  head  and  has  the  appearance 
of  a  gland-like  structure.  In  embryos  of  Bufo,  Beraneck24 
observed  close  to  the  commissura  habenularis  a  small  prominence 
which  early  disappears;  this  he  identified  as  the  anlage  of  a 
transitory  parapineal  organ.  For  the  most  part,  however, 
observers  have  found  that  a  single  evagination  in  the  roof-plate 
marks  the  anlage  of  the  epiphyseal  complex  (fig.  20). 


THE    PINEAL   BODY  55 

Eycleshymer,112  in  attempting  to  explain  the  unpaired  origin 
of  the  epiphysis  in  Amblystoma,  maintained  that  in  the  phylo- 
genetic  period  when  the  lateral  eyes  became  implicated  by  the 
closing  of  the  neural  fold,  a  median  eye  would  arise  and  thus 
become  most  highly  functional  during  the  time  when  the  lateral 
eyes  were  little,  if  at  all,  functional.  Cameron,50  working  with 
the  embryos  of  Rana,  Bufo,  and  Triton,  concluded  that  the 


Fig.  20  Anlage  of  the  epiphyseal  complex  in  a  13  mm.  embryo  of  Salamandra 
maculata,  according  to  Kupffer,  1893. 

Ls.,  lamina  terminalis;  Pf.,  paraphysis;  V.,  velum  transversum;  Ds.,  dorsal 
sac;  Ch.,  commissura  habenularis;  Po.,  pineal  organ;  Sch.,  pars  intercalaris  pos- 
terior; Cp.,  commissura  posterior;  M,  midbrain. 

epiphysis  in  amphibia  arises  as  two  primary  outgrowths  from 
the  roof  of  the  forebrain  (fig.  21). 

These  are  placed  one  on  either  side  of  the  mesial  plane.  The 
outgrowth  situated  to  the  right  of  the  middle  line  disappears  at 
an  early  age  by  blending  with  the  left  outgrowth.  The  latter 
shows  most  active  growth  so  that  the  epiphyseal  opening  becomes 
situated  to  the  left  of  the  mesial  plane.  The  left  outgrowth, 


56 


FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 


however,  is  the  more  important  of  the  two  in  amphibia.  Cam- 
eron believes  that  there  is  evidence  of  a  bilateral  origin  to  be 
found  in  the  later  stages  of  amphibian  development.  The 
portion  of  the  anlage  in  connection  with  the  superior  commissure 
corresponds  to  the  parietal  eye  of  Sphenodon  while  the  remainder 
corresponds  to  the  epiphyseal  stalk.  From  this  evidence  in 
amphibia  he  is  inclined  to  agree  with  Dendy86  that  the  ancestors 
of  vertebrates  must  have  possessed  a  pair  of  parietal  eyes  (figs. 
22  and  23). 


Fig.  21  Anlage  of  the  epiphyseal  complex  in  an  embryo  of  Triton  cristatus, 
according  to  deGraaf,  1886. 

Ch.,  commissura  habenularis;  R.,  recessus  and  pineal  organ;  Cp.,  commissura 
posterior;  M.,  midbrain;  Epid.,  epidermis;  Cor.,  corium. 

6.  The  development  of  the  epiphyseal  complex  in  reptilia 

The  fact  that  in  Prosaurians  and  Saurians  a  well  developed 
«ye  is  found  in  many  forms  has  been  the  cause  of  much  dis- 
cussion as  to  the  embryolgical  process  by  means  of  which  this 
structure  is  differentiated  from  the  epiphyseal  complex.  Accord- 
ing to  the  older  view,  the  parietal  eye  arose,  as  in  the  case  of  the 
isolated  end-vesicle  of  amphibia,  by  a  process  of  constriction 
from  the  terminal  portion  of  the  pineal  organ.  Subsequently 
the  view  was  advanced  that  instead  of  a  process  of  constriction 


THE    PINEAL   BODY 


57 


it  was  rather  a  subdivision  of  a  single  evagination  from  the  roof- 
plate  which  gave  rise  to  the  parietal  eye;  more  recently,  however, 
the  opinion  has  been  expressed  by  several  observers,  that  the 
parietal  eye  owes  its  existence  to  an  anlage  quite  independent 
from  that  of  the  pineal  organ  and  situated  anterior  to  the  latter 
in  its  point  of  development  from  the  roof-plate  of  the  inter- 
brain.  The  fact  that  the  parietal  eye  was  not  the  constricted 
end  of  the  epiphysis,  but  was  independently  connected  by 


Fig.  22    Anlage  of  the  epiphyseal  complex  in  an  11  mm  larva  of  Bufo  vulgaris 
according  to  Beraneck,  1893. 

Po.,  pineal  organ  (end-vesicle);  Ep.,  proximal  portion. 

means  of  a  nerve  of  its  own  to  the  roof  of  the  brain,  was  shown 
conclusively  by  Strahl  and  Martin383  as  well  as  Beraneck,23  who 
was  first  to  call  attention  to  the  nerve  fibers  connecting  the 
parietal  eye  with  the  brain,  namely,  the  parietal  nerve.  Having 
thus  dispensed  with  the  idea  that  the  parietal  eye  was  merely  a 
constricted  portion  of  the  end  of  the  epiphysis  proper,  it  re- 
mained for  subsequent  investigation  to  demonstrate  the  actual 
process  by  means  of  which  the  parietal  eye  arose.  Advocating 
the  view  that  the  anlage  of  the  epiphyseal  complex  in  Reptilia, 
and  particularly  in  the  Saurian  and  Prosaurian  forms,  is  an 
evagination  subdivided  into  an  anterior  and  a  posterior  compart- 


58 


FREDERICK   TILNEY   AND    LUTHER    F.    WARREN 


ment,  there  has  been  assembled  a  formidable  array  of  evidence* 
Hoffmann/86  from  his  observations  on  Lacerta  agilis,  Strahl  and 
Martin,383  in  Anguis  and  Lacerta  vivipara,  Francotte,127  on 
Lacerta  vivipara,  Klinckowstroem,207  in  Iguana,  McKay,255  in 
Grammatophora  muricata,  and  Schauinsland,346  in  Sphenodon 
all  advocate  this  view  (fig.  24). 


Fig.  23  Anlage  of  the  epiphyseal  complex  in  a  12mm.  larva  of  Buf o  vulgaris 
according  to  Beraneck,  1893. 

Po.,  pineal  organ;  Ep.,  proximal  portion. 

Beraneck,23  on  the  other  hand,  in  his  well-known  work  upon 
the  parietal  eye  and  the  morphology  of  the  third  eye  of  verte- 
brates, concludes  that  the  parietal  eye  should  not  be  considered 
as  a  simple  diverticulum  of  the  pineal  gland.  In  Lacerta  and 
Anguis  it  constitutes  an  independent  organ  which  develops  from 
the  thalamencephalon  as  the  epiphysis,  but  develops  parallel  to 
the  latter  not  dependent  upon  it.  The  parietal  eye  is  attached 
by  a  neural  fasciculus  which  is  transitory  and  not  in  any  sense 
derived  from  the  epiphysis  (fig.  25). 


THE    PINEAL   BODY  59 

It  is  part  of  the  small  mass  of  cells  situated  between  the  base 
of  the  pineal  gland  and  the  first  fold  of  the  chorioid  plexus.  The 
unpaired  eye  is  an  evagination  of  the  dorsal  wall  of  the  inter- 
brain  and  constitutes,  an  optic  vesicle.  The  separation  which 
sometimes  occurs  between  the  crystalline  and  retina  of  this 
vesicle  is  ordinarily  unilateral,  rarely  bilateral.  It  appears 
relatively  late  in  embryonic  development  and  should  not  be  con- 
sidered a  proof  of  the  duality  of  origin  of  the  parietal  organ  as 
Beard18  has  considered  it.  The  unpaired  eye  does  not  occur  in 
chordates  nor  does  it  have  its  homologue  in  the  other  branches 
of  the  metazoa.  Sometimes  it  has  its  physiological  analogue  in 
the  median  eye  of  Crustaceans.  It  is  an  ancestral  organ  which 
was  atrophied  in  the  majority  of  extant  forms  of  the  different 


Fig.  24    Two  successive  stages  in  the  development  of  the  epiphyseal  complex 
in  Lacerta  vivipara,  according  to  Francotte,  1896. 

Pa.,  parapineal  organ;  Po.,  pineal  organ;  M.,  midbrain. 

branches  of  the  chordate  phylum.  The  primitive  optic  vesicle  is 
still  recognizable  in  cyclostomes  and  Saurians;  it  is  rudimentary 
in  teleosts  and  amphibians,  but  appears  to  be  absent  in  sela- 
chians. On  the  other  hand,  the  epiphysis  in  these  latter  forms 
is  very  long  and  broadened  at  its  distal  extremity  without  form- 
ing an  optic  vesicle.  The  epiphysis  is  also  derived  from  an 
evagination  of  the  interbrain  roof.  It  does  not  represent  the 
optic  pedicle  of  the  parietal  eye.  It  is  an  organ  sui  generis 
whose  function  is  still  unknown.  It  reveals  no  marked  sensory 
characteristics  even  in  selachians  where  it  is  markedly  .devel- 
oped. It  appears  in  the  entire  series  of  vertebrates  and  is  an 
ancestral  organ.  The  paired  eye  and  epiphysis  appertain  to  the 
interbrain  while  the  paraphysis  is  part  of  the  endbrain.  This 


60 


FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 


paraphysis  shows  no  features  of  sensory  function.  Of  these 
three  encephalic  diverticula  from  the  roof-plate  in  Saurians, 
the  parietal  eye  alone  seems  to  have  had  ancestral  sensory 
function  (fig.  26). 

In  a  later  communication,  combating  the  contention  of  Klinck- 
owstroem207  to  the  effect  that  the  evolutional  process  observed 
in  Anguis  is  normal  and  more  primitive  while  that  in  Lacerta 
is  a  simple  modification  of  this .  primitive  form,  Beraneck25  pro- 


Fig. 


The  epiphyseal  complex  in  a  27  mm.  embryo  of  Anguis  fragilis,  ac- 


cording to  Beraneck,  1892. 

Pf.,  paraphysis;  V.,  velum  transversum;  Ds.,  dorsal  sac;  Ch.,  commissura  ha- 
benularis;  Npar.,  nervus  parapinealis;  Pa.,  parapineal  organ;  Ep.,  pineal  organ; 
Sch.,  pars  intercalaris  posterior;  Cp.,  commissura  posterior. 

posed  this  question,  "If  in  Anguis  the  parietal  eye  is  only  a 
differentiation  of  the  distal  extremity  of  the  epiphysis,  how  in 
Lacena  does  this  visual  organ  develop  parallel  to  the  epiphysis 
and  not  dependent  upon  it?"  Beraneck  maintains  that  Klinc- 
kowstroem  escapes  the  difficulty  proposed  by  this  question  in 
claiming  that  the  pineal  eye  of  Iguana  and  Lacerta  upon  the 
one  hand  and  Anguis  upon  the  other  take  origin  from  different 
parts  of  the  epiphyseal  evagination.  Beraneck  formulates  the 
hypothesis  that  the  parietal  eye  and  epiphysis  represent  in 


THE    PINEAL    BODY 


61 


Lacerta  two  distinct  evaginations  of  the  thalamencephalic  roof. 
If  they  appear  to  be  different  in  Iguana  and  Anguis  that  is  due  to 
secondary  modifications  of  this  region.  The  evolution  of  the 
parietal  eye  in  Iguana  is  intermediate  between  the  conditions 
observed  in  Lacerta  and  Anguis.  In  his  conclusion,  Beraneck 
emphasizes  his  belief  that  the  embryonic  facts  contradict  the 


Ch 


Fig.  26  Frontal  section  showing  epiphyseal  complex  in  a  26-day  old  Iguana 
tuberculata,  according  to  Klinckowstroem,  1894. 

P/.,  paraphysis;  Ds.,  dorsal  sac;  Npar.,  nervus  parapinealis;  Ep.,  proximal 
portion  of  pineal  organ;  Ch  ,  commissura  habenularis;  Af.,  midbrain 

epiphyseal  origin  of  the  parietal  eye  in  Saurians  and  confirm 
the  hypothesis  of  its  embryonic  individuality.  Leydig238  in 
1891  confirmed  the  view  of  Beraneck  in  Lacerta  agilis.  Bendy86 
also  states  that  the  parietal  eye  and  what  he  calls  the  parietal 
stalk  arise  from  two  distinct  evaginations  in  the  roof-plate  of 
the  interbrain.  By  parietal  stalk,  Bendy  refers  to  the  portion 
of  the  epiphyseal  complex  here  referred  to  as  the  pineal  organ. 


§•7    /W  /        *y    /^t 

•</.%     /     fiO 

/  '  i ••      i 


M 


SchJ 


M 


THE    PINEAL   BODY 


63 


The  development  of  the  epiphyseal  complex  in  Ophidia,  Chelonia, 
and  Crocodilia.  The  embryonic  description  which  holds  good 
for  the  more  primitive  forms  of  reptiles  must  be  much  modified 
in  dealing  with  the  more  highly  organized  and  modern  forms  of 
this  class.  Hoffmann186  showed  that  in  these  reptiles  the  anlage 
of  the  epiphyseal  complex  is  laid  down  as  a  single  evagination 


AT.   ,  . 


Fig.  29  The  epiphyseal  complex  in  Tropidonotus  natrix,  according  to  Stud- 
nicka,  1893. 

Pf.,  paraphysis;  Ds.,  dorsal  sac;  Ch..  commissura  habenularis;  Ep.,  proximal 
portion  of  pineal  organ;  R.,  recessus  pinealis.  Cp.,  commissura  posterior;  M., 
midbrain. 

from  the  roof-plate  immediately  anterior  to  the  posterior  com- 
missure. This  hollow  evagination  is  ultimately  transformed 
into  a  solid  body.  Such  a  transformation  has  been  shown  by 
Ley  dig210  and  Studnicka389  in  Tropidonotus  (figs.  29  and  30). 

Fig.  27  The  epiphyseal  complex  in  a  31  mm.  embryo  of  Gehyra  oceanica,  ac- 
cording to  Stemmler,  1900. 

Pf.,  paraphysis;  V.,  velum  transversum;  Ds.,  dorsal  sac;  Ch.,  commissura 
habenularis;  Ep.,  pineal  organ;  Cp.,  posterior  commissure;  M.,  midbrain. 

Fig.  28  The  epiphyseal  complex  in  a  33  mm .  embryo  of  Platydactylus  muralis, 
according  to  Melchers,  1899. 

Pf.,  paraphysis;  Ds.,  dorsal  sac;  Ch.,  commissura  habenularis;  Ep.,  pmea 
organ;  Sch.,  pars  intercalaris  posterior;  M,  midbrain. 


64 


FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 


The  cells  constituting  this  solid  organ  arrange  themselves 
more  or  less  in  alveolar  or  aciniform  cell  groups  and  the  whole 
body  ultimately  becomes  attached  to  the  roof -plate  by  means  of 
a  thin  stalk  or  peduncle.  No  evidence  of  an  anterior  evagina- 
tion  representing  the  parapineal  element  has  been  observed  nor 
is  there  any  evidence  to  show  that  any  effort  toward  the  devel- 
opment of  the  parietal  eye  in  Ophidia,  Chelonia,  or  Crocodilia 


Fig.  30  The  epiphyseal  complex  in  an  older  Tropidonotus  embryo,  according 
to  Leydig,  1897. 

P/.,  Paraphysis;  Ds.,  dorsal  sac;  Ch.,  commissura  habemilaris;  Ep.,  proximal 
portion  of  pineal  gland. 

is  present.  In  fact,  in  the  latter  forms,  namely,  Crocodilia,  the 
entire  epiphyseal  complex  is  said  to  be  wanting  and  no  evidence 
of  its  development  occurs  at  any  time  during  ontogenesis  (figs. 
31  and  32). 

One  of  the  authors,  studying  the  development  of  the  epiphysis 
in  turtles,  reconstructed  the  forebrain  of  Thalassochelys  caretia 
in  several  stages.  The  conditions  in  the  30  mm.  embryo  are 
shown  in  figure  33.  Here  the  pineal  region  consists  of  a  well- 


(./» 


Hm 


M 


Fig.  31     The  epiphyseal  complex  in  an  old  embryo  of  Chelydra  serpentina, 
according  to  Humphrey,  1894. 

Pf.,  paraphysis;  V.,  velum  transversum;  Ds.,  dorsal  sac;  Ep.,  pineal  organ;  Cp., 
posterior  commissure. 

Fig.  32     The  pineal  region  in  an  old  embryo  of  Caiman  niger,  according  to 
Voeltzkow,  1903. 

Hm.,  hemisphere;  Pf.,  paraphysis;  Ds.,  dorsal  sac;  Ch.,  commissura  habenu- 
laris;  Af,  midbrain. 

65 

MEMOIR   NO.   9 


66 


FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 


marked  paraphyseal  evagination,  a  velum  transversum,  a  dorsal 
sac,  a  commissura  habenularis,  and  a  single  thick-walled  anlage  of 
the  pineal  body  whose  apex  is  directed  cephalad.  The  most 
caudal  structure  in  the  pineal  region  is  the  posterior  commissure. 


Pf 


Fig.  33     Reconstruction  of  a  30  mm.  embryo  of  Thalassochelys  caretta. 

Ls.,  lamina  terminalis;  Pf.,  paraphysis;  V.,  velum  transversum;  Ds.,  dorsal 
sac;  Ch.,  commissura  habenularis;  Po.,  epiphysis;  Cp.,  posterior  commissure;  R., 
Rathke  pocket. 


THE    PINEAL   BODY 


67 


7.  The  development  of  the  epiphyseal  complex  in  aves 


In  birds,  the  anlage  of  the  epiphyseal  complex  makes  its  first 
appearance  as  a  simple  and  single  evagination.  This  was  first 
observed  and  described  by  Reissner329  in  1851  and  called  by 
Reichert326  in  1859  the  recessus  pinealis.  Lieberktihn242  in  1871 
identified  this  evagination  in  birds  as  the  anlage  of  the  epiphysis. 

In  many  instances  the  presence  of  a  double  evagination  of 
the  roof-plate  has  been  reported  in  the  anlage  of  the  epiphysis 
in  birds.  Saint  Remy340  in  1897  found  on  either  side  of  the  still 
unclosed  neural  tube  a  small  evagination  in  the  region  of  the 


Fig.  34    The  epiphyseal  complex  in  an  8-day  embryo  of  Anas  domesticata, 
according  to  Hechscher,  1890. 

epiphyseal  anlage.  This  observation  was  made  upon  Gallus, 
but  Parker301  in  1892,  in  Apieryx,  and  Klinckowstroem206  in 
1892,  in  Larus,  mentioned  an  evagination  in  front  of  the  epi- 
physeal anlage.  Hill181  in  1900  observed  in  a  closed  neural  tube 
two  such  evaginations.  Whether  it  is  justified  to  consider  the 
anlage  of  the  epiphysis  in  birds  as  bilateral  or  double  or  whether 
one  of  these  evaginations  represent  the  remnant  of  the  para- 
pineal  organ,  is  a  difficult  question  to  decide.  By  many  these 
reduplications  in  the  anlage  are  considered  as  pathological  since 
they  occur  only  in  isolated  instances  of  the  several  species 
described.  The  most  common  form  in  which  the  anlage  in  birds 


68 


FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 


presents  itself  is  a  single  evagination  in  front  of  the  posterior 
commissure.  The  further  differentiation  of  the  epiphysis  is 
given  by  Lieberkiihn242  in  Gallus  and  also  in  much  more  detail  by 
Mihalkovicz274  in  1874  and  1877.  According  to  the  description 
of  the  latter,  the  principal  change  from  the  original  saccular 
evagination  in  the  roof-plate  consists  in  the  conversion  of  the 
original  sac  into  a  folliculated  structure  which  presents  many 
alveoliform  cell  groups  as  a  result  of  the  rapid  proliferation  in 
the  walls  of  the  original  saccular  anlage.  Henrichs  ('96) 173 
found  that  the  follicles  first  developed  as  hollow  buds  in  com- 
munication with  the  main  cavity  of  the  original  epiphyseal 
anlage,  Later  these  buds  become  branched  and  in  this  way  a 
rich  follicular  system  is  developed. 


Fig.  35  The  epiphyseal  complex  in  an  embryo  of  Sterna  hirundo.  according  to 
Klinckowstroem,"1891. 

According  to  Henrichs,  the  paraphysis  first  appears  as  a  solid 
sprout  and  later  acquires  a  lumen.  Cameron51  showed  in  the 
chick  that  the  epiphyseal  anlage  is  a  double  outgrowth,  the  left 
being  the  larger.  These  two  evaginations  ultimately  coalesce. 
Practically  the  same  condition  is  observed  in  amphibia.  Gar- 
jano144  makes  the  observation  which  in  the  main  covers  the  con- 
ditions observed  in  birds,  namely,  that  as  compared  with  the 
lower  vertebrates  the  pineal  body  is  a  profoundly  altered  organ 
in  birds  and  mammals. 

One  of  the  authors  in  a  recent  work  on  the  diencephalon  re- 
produces illustrations  of  reconstruction  models  which  show  the 
development  in  the  pineal  region  of  Gallus  gallus.  The  first 


THE    PINEAL   BODY 


69 


evidence  of  the  epiphyseal  complex  in  the  chick  makes  its  appear- 
ance at  five  days  and  twenty  hours  as  a  sprout  from  the  caudal 
extremity  of  the  interbrain  roof-plate.  This  sprout  contains  a 
narrow  canal  and  at  this  very  early  period  shows  an  apparent 
differentiation  into  an  expanded  distal  portion,  a  stalk,  and  an 
expanded  proximal  portion. 


Fig.  36  Mesial  view  of  forebrain  reconstruction  of  chick  of  5  days  and  20 
hours.  X  100.  The  unshaded  area  shows  the  cut  surfaces  of  the  reconstruction, 
according  to  Tilney,  1915. 

2,  chiasmatic  process;  4,  chiasm;  7,  epiphysis;  13,  infundibular  process;  20, 
lamina  terminalis;  25,  mamrnillary  region;  32,  post-chiasmatic  eminence;  33,  post- 
chiasmatic  recess;  36,  post-infundibular  eminence;  38,  pre-optic  recess;  39,  para- 
physis;  41,  supra-optic  crest;  42,  supra-optic  recess;  44,  telencephalon;  45,  tuber- 
culum  postero-superius;  46,  tubercle  of  the  floor  of  Schulte. 


70 


FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 


At  this  time  the  pineal  region  presents  a  well-marked  para- 
physis,  a  velum  transversum,  and  a  dorsal  sac.  At  the  stage  of 
eight  days  in  the  chick  a  marked  change  is  noticed,  for  at  this 
period  of  development  the  pineal  anlage  has  the  appearance  of  a 
wide  and  expansive  evagination  in  free  communication  with  the 
third  ventricle. 


Fig  37  Mesial  view  of  forebrain  reconstruction  of  chick  of  8  days  X  50. 
The  unshaded  area  shows  the  cut  surfaces  of  the  reconstruction,  according  to 
Tilney,  1915. 

2,  chiasmatic  process;  3,  cerebellum;  4,  chiasm;  7,  epiphysis;  9,  foramen  of 
Monro;  11,  infundibular  stem;  12,  infundibular  canal;  13,  infundibular  process; 
24,  midbrain;  25,  mammillary  region;  26,  mammillary  recess;  32,  post-chiasmatic 
eminence;  35,  post-infundibular  recess;  36,  post-infundibular  eminence;  38,  pre- 
chiasmatic  recess;  39,  paraphysis;  41,  supra-optic  crest;  42,  supra-optic  recess; 
44,  telencephalon. 

The  brain  of  the  chick  at  fourteen  days  and  eighteen  hours 
shows  a  marked  alteration  in  the  pineal  region,  as  a  result  of 
which  the  development  of  the  epiphysis  seems  to  overshadow  all 
other  structures  in  this  region.  The  walls  of  the  evagination 
which  characterize  the  pineal  organ  in  the  eight-day  chick  have 
become  greatly  thickened  near  the  distal  extremity  of  the  epi- 
physis so  that  now  this  portion  of  the  organ  is  practically  solid 


THE   PINEAL   BODY 


71 


with  the  exception  of  a  very  small  lumen  which  extends  almost 
throughout  its  entire  extent.  A  very  large  pineal  recess  is 
present.  The  dorsal  sac  and  paraphysis  are  both  much  reduced 
in  size.  There  is  no  evidence  of  any  distal  portion  of  the  pineal 
organ  at  this  period.  No  sign  of  an  evagination  or  anlage  which 
might  be  interpreted  as  the  parapineal  organ  was  found  in  this 
study. 


39 


Fig.  38  Mesial  view  of  forebrain  reconstruction  of  14  days  and  18  hours  chick. 
X  25,  according  to  Tilney,  1915. 

1,  aqueduct  of  Sylvius;  2,  chiasmatic  process;  3,  cerebellum;  4,  optic  chiasm;  7, 
epiphysis;  9,  foramen  of  Monro;  12,  infundibular  canal;  14,  infundibular  process, 
saccular  surface;  15,  infundibular  process,  pituitary  surface;  24,  midbrain;  26, 
mammillary  recess;  27,  mammillary  body;  32,  post-chiasmatic  eminence;  33,  post- 
chiasmatic  recess;  36,  post-infundibular  eminence;  38,  pre-chiasmatic  recess; 39, 
paraphysis;  41,  supra-optic  crest;  42,  supra-optic  recess;  44,  telencephalon. 


72  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

8.  The  development  of  the  epiphyseal  complex  in  mammals 

The  only  portion  of  the  epiphyseal  complex  which  appears  in 
the  anlr,ge  in  mammals  is,  in  all  probability,  the  proximal  part 
of  the  pineal  organ,  for  there  is  no  evidence  of  the  anterior  or 
parapineal  element.  Mihalkovicz275  in  1877  gave  a  description 
of  the  development  of  the  organ  in  mammals  and  called  attention 
to  the  fact  that  it  resembled  very  closely  that  of  birds.  At  first 
the  anlage  is  a  simple  evagination,  then  several  lateral  diverticula 
about  the  same  size  make  their  appearance  and  later  give  rise  to 
many  follicles.  The  lumen  of  each  follicle  from  the  beginning  is 
smaller  than  that  in  birds  and  ultimately  is  obliterated  so  that 
there  are  finally  solid  follicles  surrounded  by  connective  tissue 
and  blood  vessels.  The  epiphysis  always  retains  its  connection 
with  the  interbrain  by  means  of  a  set  of  peduncles.  These 
peduncles  vary  in  their  arrangement  and  number  according  to 
the  form  of  the  animal.  In  man  they  are  described  by  Testut393 
as  being  three  pairs,  known  respectively  as  the  superior,  middle, 
and  inferior  peduncles  of  the  pineal  body.  Mihalkovicz  gave 
his  description  of  the  relations  of  the  anlage  to  the  roof-plate  as 
he  observed  them  particularly  in  the  rabbit. 

Kraushaar221  in  1885  confirmed  these  findings  in  the  mouse 
and  Kolliker211  in  1879  in  the  rabbit  and  'sheep.  d'Erchia109  in 
1896  found  that  the  epiphysis  in  the  guinea-pig  is  laid  down  as 
a  solid  bud  or  sprout,  while  in  man  it  has  in  its  anlage  a  small 
lumen  from  the  beginning  (fig.  39). 

Neumeyer282  in  1899  found  in  the  rabbit  that  the  epiphyseal 
anlage  was  a  long,  tubular  structure  with  a  narrow  lumen  and 
considerably  convoluted.  The  original  lumen  of  the  anlage  is 
ultimately  reduced  until  it  occupies  the  proximal  portion  only 
where  it  is  known  as  the  recessus  pinealis,  according  to  Reichert,326 
or  the  recessus  infrapinealis,  according  to  Mihalkovicz.275  This 
distinction  takes  account  of  the  description  already  given  by 
Reichert  of  the  suprapineal  recess. 

In  studying  the  development  of  the  diencephalon  in  the 
domestic  cat  one  of  the  authors  illustrates  by  reconstruction 
models  of  the  following  embryos:  In  Felis  domeslica,  the  pineal 


THE    PINEAL   BODY 


73 


organ  shows  the  first  appearance  of  the  epiphyseal  complex  at 
the  stage  of  30  mm.  embryo  where  it  takes  the  form  of  a  wide, 
single  evagination  immediately  cephalad  to  the  posterior  com- 
missure. This  evagination  contains  a  recess  in  free  communica- 
tion with  the  third  ventricle  (fig.  40). 

In  a  cat  embryo  of  51  mm.  a  notable  change  has  taken  place 
in  the  epiphyseal  anlage  shown  in  the  fact  that  the  original 
single  evagination  has  now  become  subdivided  into  two  smaller 
sacs  separated  by  a  marked  thickening  in  the  original  diver- 
ticulum.  This  is  shown  in  figure  41. 


EP 


Fig.  39    The  pineal  body  in  Cavia  cobaya,  according  to  d'Erchia,  1896. 
Ds  ,  dorsal  sac;  Ch.,  commissura  habenularis;  Sch.,  pars  intercalaris;  Ep., 
epiphysis  cerebri;  M,  midbrain. 

In  so  far  as  is  known  no  similar  occurrence  has  been  noted  in 
mammals  with  the  exception  of  a  single  report  by  Cut  ore74  in 
the  new-born  Bos  taurus  in  which  two  distinct  evaginations  in 
the  epiphyseal  complex  were  observed.  This  appearance  was 
interpreted  by  Cutore  as  indicative  of  an  anlage  both  for  the 
pineal  and  parapineal  organs,  and  if  such  an  interpretation 
seems  acceptable,  it  might  be  applied  to  the  appearances  just 
mentioned  in  the  embryos  of  the  domestic  cat.  The  tendency 
for  this  double  diverticulum  to  persist  through  the  development 


74 


FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 


of  the  later  stages  in  the  cat  is  shown  in  figure  42,  illustrating  the 
conditions  in  a  70  mm.  embryo.  Models  by  one  of  the  authors 
show  the  existence  of  this  twofold  structure  in  the  cat  as  late  as 
120  mm.  embryo. 


39 


25 


35 


Fig.  40  Mesial  view  of  forebrain  reconstruction  of  30  mm.  cat  embryo.  X  50. 
The  unshaded  area  shows  the  cut  surfaces  of  the  reconstruction,  according  to 
Tilney,  1915 

2,  chiasmatic  process;  4,  chiasm;  5,  corpus  interpedunculare;  7,  epiphysis;  9, 
foramen  of  Monro;  11,  infundibular  stem;  12,  infundibular  canal;  13,  infundibular 
process;  20,  lamina  terminalis;  25,  mammillary  region;  32,  post-chiasmatic  emi- 
nence; 33,  post-chiasmatic  recess;  34,  post-infundibular  eminence;  35,  post-in- 
fundibular recess;  39,  dorsal  sac;  40,  recess  of  the  infundibular  process;  41  supra- 
optic  crest;  42,  supra-optic  recess. 

The  most  recent  study  of  the  pineal  region  in  mammals  is  that 
of  John  Warren,417  in  which  he  brings  to  a  conclusion  his  excel- 
lent series  of  papers  upon  the  interpretation  of  this  region  of 
the  brain  in  vertebrates.  Of  the  human  embryo  he  gives  the 
following  description  (fig.  43) : 


THE    PINEAL   BODY 


75 


The  primary  arches  can  be  demonstrated  in  early  human  embryos 
from  10  to  15  mm.  in  length. 

Of  the  embryos  of  15  mm.  and  over  examined  there  were  about  thirty 
in  which  the  brain  was  in  suitable  condition  to  warrant  making  obser- 
vations, and  in  addition  to  these  a  number  of  others  were  studied  but 
excluded  on  account  of  injury  or  distortion  of  the  forebrain.  In  the 
thirty  specimens  only  eight  showed  any  possible  signs  of  a  paraphysis 
and  most  of  these  were  mostly  rudimentary  in  character.  By  counting, 
every  possible  case  we  get  a  result  of  27  per  cent.  The  fact  remains, 


-20 


Fig.  41  Mesial  view  of  forebrain  reconstruction  of  51mm.  cat  embryo  X  50. 
The  unshaded  area  shows  the  cut  surfaces  of  the  reconstruction,  according  to 
Tilney,  1915. 

2,  chiasmatic  process;  4,  chiasm;  5,  corpus  interpedunculare;  7,  epiphysis;  9, 
foramen  of  Monro;  11,  infundibular  stem;  13,  infundibular  process;  20,  lamina 
terminalis;  27,  mammillary  body;  32,  post-chiasmatic  eminence;  33,  post-chias- 
matic  recess;  35,  post-infundibular  recess;  36,  post-infundibular  evagination;  39, 
dorsal  sac;  40,  recess  of  the  infundibular  process;  42,  supra-optic  recess 


76 


FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 


however,  that  the  structure  can  be  found  in  human  embryos,  though 
in  a  rudimentary  and  inconstant  condition. 

The  so-called  postvelar  tubules  or  diverticula  can  be  clearly  fol- 
lowed in  every  degree  of  complexity  in  embryos  of  19  mm.  up  to  44 
mm.  and  appear  in  every  specimen  studied  in  those  stages.  They 


24 


42 


38 


42  Mesial  view  of  forebrain  reconstruction  of  70  mm.  cat  embryo.  X  25. 
The  unshaded  area  shows  the  cut  surface  of  the  reconstruction.  According  to 
Tilney,  1915. 

2,  chiasmatic  process;  4,  chiasm;  5,  corpus  interpedunculare;  7,  epiphysis;  9, 
foramen  of  Monro;  13,  infundibular  process;  24,  midbrain;  27,  mammillary  body; 
32,  post-chiasmatic  eminence;  33,  post-chiasmatic  recess;  34,  post-infundibular 
eminence;  35,  post-infundibular  recess;  38,  pre-chiasmatic  recess;  40,  recess  of 
infundibular  process;  41,  supra-optic  crest;  42,  supra-optic  recess. 

begin  at  the  diencephalic  lip  of  the  velum,  have  definite  limits  and 
involve  a  relatively  short  extent  of  the  oral  end  of  the  diencephalic 
roof-plate.  They  always  appear  as  outgrowths  from  the  brain  roof 
and  are  to  be  distinguished  from  ingrowths  due  to  plexus  formation. 

Warren's417  description  of  the  conditions  in  the  sheep  is  as 
follows : 


THE    PINEAL    BODY 


77 


The  primary  arches  consist  of  the  paraphyseal  arch,  the  post  velar 
arch,  the  epiphyseal  arch  and  the  pars  intercalaris  (synencephalic  arch) 
and  together  with  the  velum  are  formed  in  the  roof  of  the  forebrain  of 
early  sheep  embryos. 

The  paraphysis  can  be  followed  in  practically  all  sheep  embryos 
from  20  mm.  up  to  48  mm.  It  is  characterized  by  its  short,  broad,  and 
irregular  outline  and  its  solid  structure,  the  cavity  being  in  most  cases 
reduced  to  a  minimum. 


P.V.A. 


Fig.  43  Reconstruction  showing  development  of  the  pineal  region  in  man.  23 
mm.  embryo,  according  to  John  Warren,  1917. 

L.T.,  lamina  terminalis;  P.,  paraphysis;  V.,  velum;  P.V.A. ,  Post-velar  arch; 
E.,  epiphysis;  P.C.,  posterior  commissure. 


78  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

The  diencephalic  choroid  plexus  and  lateral  telencephalic  plexuses 
are  well  marked  and  develop  essentially  as  described  in  other  verte- 
brates. There  is  no  trace  of  the  median  telencephalic  plexus  so  notice- 
able in  Amphibia. 

The  epiphysis  forms  a  short  hollow  stalk  with  thick  walls  and  in- 
clined slightly  backward  over  the  posterior  commissure. 

.  The  superior  and  posterior  commissures  are  formed  as  in  other 
vertebrates.  The  posterior  commissure  is  characterized  by  its  pre- 
cocious development  and  by  the  extent  that  it  invades  the  pars  inter- 
calaris  of  the  forebrain  in  early  embryos  (fig.  44). 

It  will  be  observed  that  in  the  ontogenesis  of  each  element  in 
the  epiphyseal  complex,  three  distinct  parts  may  be  discerned  in 
each  of  the  two  organs  entering  into  it.  Thus,  the  pineal  organ 
may  have  an  end-sac,  a  stalk,  and  a  proximal  portion,  and  the 
same  is  true  of  the  parapineal  organ.  Considered  in  the  light 
of  comparative  embryology,  it  will  be  seen  that  the  most  con- 
stant part  throughout  the  phylum  is  the  proximal  portion  of 
the  pineal  organ.  This,  beginning  with  a  moderate  prominence, 
as  in  the  cyclostomes,  rises  to  a  very  prominent  element  in  sela- 
chians and  maintains  this  prominence  with  somewhat  of  an 
increase  in  its  importance  throughout  the  entire  series,  with  the 
single  exception  of  crocodilia,  in  which  the  pineal  body  is  said 
by  Sorensen363  to  be  entirely  wanting.  On  the  other  hand,  the 
proximal  portion  of  the  parapineal  organ  shows  a  strikingly  low 
percentage  of  occurrence  throughout  the  phylum.  It  may 
perhaps  be  accredited  to  the  cyclostomes,  if  one  takes  into 
account  the  thickened  portion  of  the  unusually  large  commissura 
habenularis,  but  thereafter  in  the  series  it  seems  to  disappear 
entirely. 

The  next  most  constant  structure  in  the  epiphyseal  complex 
is  the  end- vesicle  of  the  pineal  organ.  This  maintains  a  high 
degree  of  prominence  in  cyclostomes,  selachians,  ganoids,  teleosts, 
urodeles  and  anura.  It  shows  a  conspicuous  tendency  to  atten- 
uate in  the  prosaurians  and  saurians  and  finally  in  the  ophidians, 
and  in  all  the  orders  thereafter  it  is  notable  for  its  absence.  The 
analogue  of  the  pineal  end-vesicle,  namely,  the  parapineal  end- 
vesicle,  is  much  more  irregular  in  its  occurrence  throughout  the 
phylum,  but  on  the  other  hand,  in  certain  forms  it  presents  such 


THE    PINEAL    BODY 


79 


striking  characteristics  as  to  make  it  one  of  the  most  prominent 
and  important  elements  in  the  epiphyseal  complex.  Its  appear- 
ance in  cyclostomes  is  almost  as  striking  as  the  pineal  end- vesicle, 
but  its  tendency  to  irregularity  is  noted  by  a  complete  absence 


P.O. 


KM. 


O.C. 


Fig.  14     Reconstruction  showing  the  development  of  the  pineal  region  of  a 
sheep  embryo  of  48.4  mm.,  according  to  John  Warren,  1917. 

'  F.M.,  foramen  of  Monro;  P.,  paraphysis;  V.,  velum;  S.C., commissura  hi 
ularis;  E.,  epiphysis;  P.O.,  posterior  commissure. 


89  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

in  the  selachians.  It  makes  a  somewhat  abortive  appearance  in 
the  ganoids  and  teleosts.  In  urodeles  and  anura  it  disappears 
altogether  but  when  again  it  does  occur  as  a  feature  of  the 
epiphyseal  complex,  it  has  assumed  such  proportions  as  to 
make  it  by  far  the  most  prominent  structure  in  this  area  of  the 
brain.  In  the  prosaurians  and  the  saurians,  it  is  a  most  con- 
spicuous element.  As  may  easily  be  presumed,  the  pineal  stalk 
and  its  analogue,  the  parapineal  stalk,  follow  very  closely  the 
frequency  of  occurrence  of  the  two  end- vesicles.  Thus  the 
pineal  stalk  is  present  in  cyclostomes,  selachians,  ganoids, 
teleosts,  urodeles,  anura,  prosaurians  and  saurians,  but  disap- 
pears in  the  higher  forms.  The  parapineal  stalk  is  present  in 
the  cyclostomes,  but  does  not  appear  in  selachians.  It  has  an 
abortive  form  in  ganoids  and  teleosts,  is  absent  in  urodeles  and 
anura,  occurs  in  its  most  marked  representation  in  prosaurians 
and  saurians,  and  thereafter  disappears  altogether. 


6.  THE  COMPARATIVE  ANATOMY  AND  HISTOLOGY  OF  THE 
EPIPHYSEAL  COMPLEX 

In  the  light  of  the  embryological  development  of  the  epiphy- 
seal complex,  the  difficulties  in  the  adult  morphology  of  these 
organs  are  much  diminished.  The  following  description  will 
deal  with  the  comparative  anatomy  and  histology  of  the  two 
epiphyseal  elements  in  the  different  classes  of  vertebrates  and 
will  be  based  upon  the  observations  of  the  different  species 
already  investigated. 

1.  The    comparative    anatomy    and    histology   of    the   epiphyseal 
complex  in  cyclostomes 

The  pineal  organ  in  cyclostomes  presents  the  three  charac- 
teristic parts,  namely,  a  proximal  portion,  a  stalk,  and  an  end- 
vesicle.  Each  of  these  is  more  or  less  highly  specialized.  The 
end-vesicle  has  the  form  of  a  small  elliptical  vesicle.  In  its  longest 
diameter  cephalocaudad,  it  is  0.35  mm.  in  length.  This  measure- 
ment was  made  in  Petromyzon  by  Studnicka.384  It  presents 


THE    PINEAL   BODY 


81 


certain  parts,  as  for  example,  a  dorsal  wall  and  a  ventral  wall, 
which  are  to  be  distinguished  from  each  other  by  certain  histo- 
logical  features.  These  two  walls  bound  a  cavity  or  lumen 
concerning  which  there  has  been  much  discussion  and  to  which 
the  name  of  atrium  is  usually  applied.  Ahlborn2  in  1883  states 
that  this  atrium  presents  a  peculiar  lacunar  appearance. 


Fig.  45  Cross  section  of  the  epiphyseal  complex  in  Petromyzon,  according  to 
Ahlborn,  1883. 

Po.,  pineal  organ;  Ds.,  dorsal  sac;  Pp.,  parapineal  organ;  Ha.,  habenular 
ganglion. 

Beard18  in  1889  thought  the  atrium  contained  a  coagulated 
fluid,  and  Owsiannikow295  in  1888  was  of  the  same  opinion. 
Gaskell,145  however,  in  1890  found  that  the  atrium  of  the  pineal 
organ  in  Ammoccetes  was  in  reality  filled  with  cellular  tissue 
and,  according  to  this  observer,  the  pineal  organ  in  these  forms 
had  a  general  structure  which  was  similar  to  the  composite 
eye  of  Arthropods.  Leydig239  in  1896  found  the  atrium  filled 
with  what  he  calls  secretory  fibers  extending  inward  from  the 
retinal  cells  of  the  organ.  Studnicka384  in  the  later  stages  of 
Ammoccetes  found  in  the  lumen  of  the  end-vesicle  a  peculiar, 

MEMOIR  NO.  9 


82 


FREDERICK    TILNEY   AND    LUTHER   F.    WARREN 


fibroid,  hyaline  substance  attached  to  the  free  end  of  the  cells  in 
the  retina.  This  took  on  the  form  of  a  coagulum  in  the  semifluid 
contents  of  the  atrium.  Later  Studnicka388  in  1899  described  in 
Petromyzon  marinus  similar  hyaline  bodies  and  showed  that  they 
were  the  thickened  extremities  of  the  retinal  cells  projecting  into 
the  lumen  of  the  end- vesicle. 


^f<^~r^'T^TT:r?~r^^ 

\ 


Pell- -i'\W 


pp 


Fig.  46    Sagittal  section  of  the  epiphyseal  complex  of  Petromyzon  flaviatilis 
showing  syncytial  masses  in  the  Atrium,  according  to  Studnicka,  1899. 
Pell.,  pellucida;  Po.,  pineal  organ;  Ret.,  retina;  Pp.,  parapineal  organ. 

In  this  way  these  processes  from  the  retinal  cells  formed  a 
virtual  syncytium  which  almost  completely  fills  the  atrium.  Of 
the  two  walls  forming  the  end-vesicle,  the  ventral  wall  presents 
certain  characteristics  which  seem  to  justify  the  recognition  in 
it  of  a  retinal  structure.  For  this  reason  the  ventral  wall  is 
known  as  the  retina  of  the  pineal  organ  in  cyclostomes.  The 
dorsal  wall  has  an  entirely  different  structural  character,  and 
because  it  is  quite  without  pigmentation  is  known  as  the  pellucida. 


THE    PINEAL   BODY  83 

The  retina  of  the  pineal  organ  in  cyclostomes  shows  its  most 
marked  development  in  embryonic  and  larval  stages.  Beard17 
in  1887  found  in  Ammocoetes  rod  cells,  and  Owsiannikow295  in 
1888  showed  in  Petromyzon  fluviatilis  that  there  were  five  dis- 
tinct layers  of  cells  and  fibers  in  the  retina.  The  first  of  these 
layers  consisted  of  nerve  fibers;  the  second,  of  large  nerve  cells; 
the  third  was  fibrous;  the  fourth  consisted  of  small  cells  inter- 
spersed among  the  large  rod-shaped  cells,  and  the  fifth  was  an 
ependymal  layer.  Gaskell145  in  1890  was  able  to  find  rod  cells 
only  in  the  retina  of  Ammoccetes,  and  he  was  of  the  opinion 
that  the  so-called  pineal  eye  in  this  form  was  a  compound  struc- 
ture in  which  the  light-receiving  bodies  were  formations  com- 
parable to  the  rhabdites  of  the  Arthropod  eye.  Studnicka 
('93)384  recognized  four  layers  of  cells  and  fibers  in  the  retina  of 
cyclostomes.  The  first  of  these  was  a  layer  of  nerve  fibers,  the 
second  were  basal  cells,  the  third  small  cells,  and  the  fourth, 
large  cylindrical  cells.  Leydig239  in  1896  found  two  types  of 
cells,  an  inner  cylindrical  and  an  outer  layer  of  round  cells. 
Retzius,331B  however,  in  1895,  could  find  no  evidence  of  the  sensory 
organ  in  the  so-called  pineal  eye  of  cyclostomes  and  he  did  not 
consider  it  to  be  an  eye.  Mayer264  in  1897  found  ganglionic 
cells  in  the  retina,  and  Studnicka388  in  1899  found  still  more 
evidence  of  the  retinal  nature  of  the  ventral  wall  of  the  end- 
vesicle. 

The  pellucida  becomes  best  developed  in  Petromyzon  marinus, 
for  the  dorsal  wall  of  the  pineal  organ  appears  in  the  more  or  less 
constant  form  of  a  plane  or  convexed  lens,  the  flattened  surface 
of  which  is  ectally  directed.  In  Petromyzon  planeri  and  fluvia- 
tilis, the  pellucida  is  extremely  irregular  in  its  thickness  as  well 
as  in  its  form.  It  must  not,  therefore,  be  maintained  that  even 
in  those  forms  where  the  pellucida  has  a  lenticular  shape  and 
arrangement  that  it  is  actually  a  lens  structure.  One  feature 
about  it,  however,  suggests  that  it  is  an  organ  designed  for  the 
transmission  of  light  rays,  namely,  its  almost  complete  lack  of 
pigment  except  perhaps  at  the  peripheral  edges  where  it  passes 
over  into  the  ventral  wall  or  so-called  retina  of  the  pineal  eye. 
This  lack  of  pigment  led  Carriere57  in  1890  to  call  the  dorsal  wall 


84 


FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 


of  the  pineal  organ  the  pellucida.  Histologically  the  pellucida 
is,  according  to  Ahlborn2  made  up  of  cells  of  considerable  size 
together  with  connective  tissue.  Owsiannikow296  found  both 
fibers  and  small  cells.  Whitwell421  and  Beard18  in  1888  found 


.        i 


Fig.  47    Retina  and  pellucida  of  the  pineal  organ  in  a  full-grown  Petromyzon 
marinus,  according  to  Studnicka,  1899. 
Pell.,  pellucida;  Ret.,  retina. 

that  the  pellucida  consisted  of  cylindrical  cells.  Gaskell145  in 
1890  observed  cylindrical  and  small  cells,  and  Studnicka388  as 
well  as  Retzius331B  found  that  the  structure  was  made  up  almost 
exclusively  of  large  cylindrical  cells. 


THE    PINEAL   BODY  85 

The  white  pigment  of  the  retina.  Mayer265  in  1864  observed 
that  the  epiphyseal  complex  in  Petromyzon  contained  many 
calcium  bodies.  Subsequently  Ahlborn2  made  the  observation 
that  there  were  a  large  number  of  small  bodies  of  a  peculiar 
white  substance  which  he  called  the  white  pigment  and  regarded 
it  as  similar  to  the  brain  sand  of  the  higher  vertebrates.  This 
white  substance  filled  in  the  cells  of  the  retina  in  such  a  way  as 
to  prevent  the  passage  of  transmitted  light  and  to  give  the 
appearance  of  a  glistening  white  when  illuminated.  Accord- 
ing to  Studnicka,388  this  pigment  does  not  appear  in  Ammoccetes 
younger  than  those  of  50  mm.  in  length,  but  thereafter  gradually 
increases  in  amount  until  the  adult  form  is  attained.  Ley  dig239 
in  1896  differentiated  two  kinds  of  pigment  bodies — those  which 
are  small  in  amount,  of  a  dark  brown  black  color  and  those  of 
the  second  type  which  by  transmitted  light  appear  to  be  a 
brownish  yellow.  By  direct  light  these  pigments  appear  to  be 
white. 

The  stalk  of  the  pineal  organ  in  cyclostomes.  In  cyclostomes 
the  pineal  stalk  becomes  much  reduced  in  size  and  it  completely 
loses  its  lumen  in  the  adult.  It  becomes  conspicuous,  however, 
by  the  development  in  it  of  certain  nerve  fibers  whose  collected 
bundle  was  first  called  by  Leydig239  in  1896  the  'Zirbelnerv.' 
This  structure,  later  in  1898,  was  called  by  Gaupp147  the  tractus 
pinealis  and  finally  the  nervus  pinealis  by  Studnicka.388  This 
pineal  nerve  established  a  fiber  connection  between  the  peculiar 
organ  situated  beneath  the  roof-plate  and  known  as  the  pineal 
eye  in  cyclostomes,  and  the  roof  of  the  brain.  The  fibrous 
nature  of  its  structure  was  first  observed  by  Whitwell421  in  1888. 
Owsiannikow295  noted  that  in  addition  to  the  nerve  fibers  there 
were  to  be  observed  in  the  pineal  stalk  a  bundle  of  fine  nerve 
fibers.  The  diameter  of  these  fibers,  according  to  his  measure- 
ment, was  50  micra.  Running  with  the  nerves  were  numerous 
blood  vessels.  Gaskell145  could  not  distinguish  whether  nerve 
fibers  or  processes  of  cells  made  their  course  within  the  nerve 
sheaths.  It  was  only  at  the  entrance  of  the  nerve  into  the  eye 
that  he  found  a  lumen.  Studnicka,388  however,  maintained  that 
the  stalk  was  an  actual  nerve  and  therefore  applied  to  it  the  term 


86  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

nervus  pinealis.  He  was  able  to  trace  the  nerve  fibers  from  the 
so-called  retina  of  the  pineal  eye  into  the  stalk.  Retzius331B  in 
1895,  using  Golgi  preparations  in  Ammoccetes,  was  able  to 
demonstrate  the  actual  presence  of  nerve  fibers  of  the  pineal 
nerve  which  he  followed  from  the  pineal  organ  to  the  brain. 
This  observation  in  similar  preparations  was  confirmed  by 
Mayer264  in  1897.  Leydig239  in  1896  found  in  Petromyzon 
fluviatilis  that  nerve  fibers  were  present  only  in  the  proximal 
third  of  the  stalk,  while  Johnston195  in  1902  in  Lampelra  wilderi 
found  that  the  nerve  fibers  in  the  proximal  portion  of  the  stalk 
seemed  to  be  obliterated  in  some  preparations.  The  pineal 
nerve  has  a  definite  sheath  of  its  own  consisting  of  elements  simi- 
lar to  those  covering  the  brain.  There  is  a  membrana  limitans 
externa  composed  of  neuroglia.  Surrounding  this  is  a  layer  of 
pia  mater  and  still  more  externally  a  process  from  the  dura 
mater. 

The  central  endings  of  the  nervus  pinealis  have  been  traced 
by  Ahlborn2  and  Gaskell145  to  the  posterior  commissure.  Gaskell 
showed  that  the  nerve  was  connected  with  the  right  habenular 
ganglion  and  that  this  nerve  structure  was,  therefore,  the  optic 
ganglion  of  the  pineal  eye.  Studnicka388  followed  some  of  the 
fibers  to  the  inner  portion  of  the  posterior  commissure.  He 
thought  that  the  pineal  nerve  ended  in  the  left  habenular  ganglion 
while  the  nerve  of  the  parapineal  organ  ended  in  the  right  struc- 
ture of  this  name.  Mayer264  traced  the  fibers  by  means  of  silver 
impregnation  to  the  posterior  commissure.  The  proximal 
portion  of  the  pineal  organ  in  cyclostomes  is  much  reduced  in 
size  because  of  the  close  approximation  between  the  posterior 
commissure  and  the  commissura  habenularis.  A  small  recess, 
however,  marks  the  position  of  the  proximal  portion  in  these 
forms  and  is  situated  between  the  two  commissures  just  men- 
tioned. This  is  the  recessus  pinealis.  The  pineal  organ  in 
cyclostomes  has  been  called  the  epiphysis,  the  epiphysis  cerebri, 
and  the  superior  vesicle  of  the  epiphysis,  according  to  Ahlborn 
in  1883.* 

The  parapineal  organ  in  cyclostomes.  The  more  cephalic  of 
the  two  epiphyseal  elements  in  cyclostomes  has  been  called  by 


THE    PINEAL   BODY 


87 


Studnicka388  the  parapineal  organ.  According  to  Ahlborn,2  it 
was  the  inferior  vesicle  of  the  epiphysis.  Owsiannikow295  termed 
it  the  visceral  vesicle,  while  it  was  called  by  Kupffer222  the  para- 
physis.  It  presents  an  end-vesicle,  a  stalk,  and  a  proximal 
portion.  It  its  general  form  it  resembles  the  pineal  organ  and  is 
situated  as  a  more  or  less  distinct  vesicle  between  the  pineal 
organ  and  the  roof  of  the  brain  in  the  region  immediately  cephalad 
to  the  habenular  ganglion  and  the  commissura  habenularis. 
The  vesicular  portion  is  in  relation  with  the  habenular  ganglion, 
being  situated  dorsal  to  it,  while  the  stalk  and  proximal  portion 
are  in  relation  with  the  commissura  habenularis.  In  size  the 
parapineal  organ  is  considerably  smaller  than  the  pineal  organ, 
and  though  it  varies  considerably  in  this  respect,  the  following 
tabulation  made  by  Studnicka388  shows  the  general  dimensions 
of  the  organ  in  Ammocoetes  and  Petromyzon  planeri.  These, 
figures  apply  to  the  end-vesicles. 


PINEAL  ORGAN 

PARAPINKAL  ORGAN' 

23  mm   Ammocoetes  

mm. 
0  23 

mm. 

0  105 

26  mm   Ammocoetes 

0  15 

0  12 

30  mm   Ammocoetes 

0  15 

0  09 

49  mm   Ammocoetes  

0.22 

0  15 

94  mm   Ammocoetes 

0  24 

0  14 

117  mm.  Ammocoetes  

0.31 

0.20 

Petromyzon  planeri 

0.35 

0.25 

Ahlborn2  in  1883  found  that  the  parapineal  organ  in  general 
has  the  same  form,  although  it  is  smaller  than  the  pineal  organ 
while  the  cellular  elements  in  the  two  structures  correspond  very 
closely.  The  lumen  of  the  parapineal  organ  contains  a  fibrous 
tissue  having  many  histological  features  in  common  with  that  in 
the  pineal  organ.  Beard18  in  1889  found  the  parapineal  organ 
in  Ammocceies  only  a  little  less  developed  than  the  pineal 
organ,  in  which  opinion  Gaskell145  concurs.  In  Petromyzon 
fluviatilis,  Owsiannikow295  in  1888  found  that  the  parapineal 
organ  was  smaller  than  the  pineal  organ,  but  in  no  other  way 
different  from  the  latter.  The  end-vesicle  contained  a  retina 


88 


FREDERICK    TILNEY   AND    LUTHER    F.    WARREN 


in  which  there  were  several  layers  of  cells,  including  rod-  and 
cylindrical-shaped  cells  measuring  from  7.4  to  8.3  micra  in 
diameter.  There  were  also  some  larger  cells  scattered  among 
the  rod  cells  with  a  mean  diameter  of  14  micra.  He  found  in 
the  retina  many  nerve  fibers  which  made  their  way  into  a  definite 
fasciculus  constituting  a  parapineal  nerve.  Studnicka388  did 
not  agree  wholly  with  Owsiannikow  in  the  idea  that  the  para- 
pineal  end-vesicle  was  as  well  developed  as  the  corresponding 
structure  of  the  pineal  organ.  He  states  that  the  difference 
between  these  two  structures  is  the  fact  that  the  parapineal 


Pell 


Ret 


Fig.  48  Sagittal  section  of  the  pineal  and  parapineal  organs  in  Ammocoetes 
with  silver  impregnation,  according  to  Retzius,  1895. 

Ls.,  lamina  terminalis;  P/.,  paraphysis;  Pp.,  parapineal  organ;  Ha.,  habenular 
ganglion;  Ret.,  retina;  Pell.,  pellucida;  N .pin.,  pineal  nerve. 

end-vesicle  is  not  as  highly  developed  a  retinal  structure  as  is 
the  case  with  the  pineal  end-vesicle.  Studnicka,  however,  finds 
that  there  is  in  the  dorsal  wall  of  the  parapineal  vesicle  a  definite 
pellucida  made  up  of  several  layers  of  cells.  Those  cells  iden- 
tified in  the  retinal  layer  by  Owsiannikow295  and  Studnicka388 
-as  the  rod  cells  were  recognized  by  Retzius331B  in  1895  by  means 
of  the  Golgi  method  as  bipolar  cells. 

By  this  method  Retzius3313  was  able  to  trace  nerve  fibers  which 
took  origin  in  the  left  habenular  ganglion  and  passed  to  the 
parapineal  end -vesicle.  Leydig239  in  Petromyzon  fiuviatilis 
found  that  the  parapineal  end-vesicle  was  less  developed,  but  at 


THE    PINEAL   BODY  89 

its  base  he  was  able  to  discern  fibers  which  seemed  to  cross  to 
the  opposite  side.  These  nerve  fibers  extended  backward  from 
the  cells  in  the  parapineal  organ.  Ley  dig  was  unable  to  identify 
any  structure  which  he  considered  a  retina  or  a  lens.  The  stalk 
in  the  adult  form  becomes  reduced  to  a  mere  strand  containing 
fibers  which  by  many  authors  are  considered  to  be  nerve  fibers. 
The  primitive  lumen  present  in  the  stalk  of  the  parapineal 
organ  very  early  disappears  and  the  proximal  portion  rapidly 
becomes  inconspicuous  and  finally  is  lost  by  the  marked  develop- 
ment of  the  commissura  habenularis. 

The  majority  o;f  investigators  who  have  studied  this  part  of 
the  brain  in  cyclostomes  are  in  accord  along  several  general 
lines.  They  believe  that  the  cells  found  in  the  parapineal 
end-vesicle  are  ependymal  cells,  spindle  or  rod  cells,  and  some 
sensory  cells.  It  is  also  their  opinion  that  there  are  nerve  fibers 
connecting  these  cells  situated  among  which  are  larger  ganglionic 
elements  from  which  the  fibers  may  take  their  origin.  In  a 
general  way  the  same  constituents  occur  in  the  retina  of  the 
parapineal  organ  as  are  present  in  the  pineal  organ.  The  main 
differences  between  these  two  structures  consist  in  the  size  and 
disposition  of  their  respective  elements.  In  the  adult  the  para- 
pineal organ  is  situated  upon  the  most  anterior  portion  of  the 
membranous  forebrain  roof  while  directly  in  front  of  it  is  the 
paraphysis  and  above  it  the  pineal  vesicle.  Situated  in  this 
position  the  two  end-vesicles  of  the  epiphyseal  complex  have 
the  appearance  of  a  pair  of  eyes  which  are  rudimentary  and 
which,  in  attempting  to  assume  visual  function,  have  morpho- 
logically fallen  short  in  the  attainment  of  that  object.  It  should 
be  noted  that  their  position  places  them  in  the  midsagittal 
plane,  one  behind  the  other,  and  that  according  to  the  most 
reliable  evidence  concerning  cyclostomes  available  at  the  present 
time,  there  is  no  definite  tendency  toward  lateralization  in  one 
or  the  other  of  these  elements  in  the  epiphyseal  complex.  The 
two  end-vesicles,  practically  in  contact  with  each  other,  occupy 
a  deep  fossa  formed  by  a  depression  on  the  inner  surface  of  the 
skull.  This  fossa  is  especially  well  marked  in  adults  and  more 
particularly  in  Petromyzon  marinus. 


90  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

What  has  been  termed  a  parietal  cornea  of  the  pineal  eye  con- 
sists of  a  layer  of  almost  fiberless  tissue  of  considerable  thickness 
between  the  dorsal  surface  of  the  pial  capsule  and  the  inner 
surface  of  the  bony  depression  in  the  skull.  The  epidermis 
immediately  above  this  so-called  cornea  is  quite  without  pig- 
ment, forming  a  small,  circular  area  in  the  frontal  region  of  the 
head  situated  almost  immediately  in  the  midsagittal  line.  This 
area  was  recognized  long  before  its  significance  was  understood 
and  was  described  by  Whitwell421  in  1888,  by  Ahlborn2  in  1883, 
and  by  Gage135  in  1893.  Gaskell145  in  1890  erroneously  likened  a 
cranial  thickening  above  the  pineal  organ  in  Ammoccetes  to  the 
cuticular  lens  of  Arthropods.  Studnicka384  in  1893  found  that 
the  cornea  is  discernible  in  the  25  mm.  Ammoccetes.  Gaskell,145 
in  his  discussion  of  the  origin  of  vertebrates  from  a  crustacean- 
like  ancestor,  makes  the  statement  that  in  Ammoaztes  there 
are  two  pineal  eyes,  one,  dorsally  placed,  much  larger  and  in- 
tensely white  in  color,  lies  in  front  of  the  right  habenular  ganglion. 
The  other,  ventrally  placed,  is  an  insignificant  structure.  The 
first  is  similar  to  the  crustacean  parietal  eye  in  its  pigmentary 
character.  The  second  is  similar  to  this  eye  in  Crustacea  because 
of  the  termination  of  the  nerve  endings  with  the  attached  rhab- 
dites.  According  to  Gaskell,  the  type  of  eye  is  clearly  arthro- 
podic.  The  arrangement  of  the  nerve  endings,  the  shape  of  the 
internal  cavity,  and  the  position  and  simplicity  of  the  attached 
rhabdites  all  point  to  larval  characteristics  and,  therefore,  to  an 
ancient  type.  The  anterior  wall  is  not  a  lens.  Gaskell  believes 
the  lens  is  cuticular  in  character  and,  if  so,  this  is  all  the  more 
reason  for  believing  that  the  pineal  eye  is  definitely  arthropod  in 
type. 

Much  emphasis  has  been  laid  upon  the  occurrence  in  cyclo- 
stomes  of  these  two  structures  which  have  so  many  characteristics 
suggestive  of  visual  function.  The  statement  has  been  made 
that  this  is  competent  evidence  upon  which  to  establish  the 
claim  that  in  vertebrates  the  parietal  or  third  eye  was  primi- 
tively paired.  It  is  to  be  noted,  however,  that  in  no  other  class 
of  vertebrates  does  the  duality  of  the  parietal  visual  apparatus, 
if  such  indeed  it  may  be  considered,  attain  such  a  high  degree  of 


THE    PINEAL  BODY  91 

development.  One  or  the  other  element  of  the  epiphyseal  com- 
plex may  show  the  tendency  toward  the  development  of  visual 
characteristics,  but  in  no  other  form  do  both  of  these  elements 
take  on  these  features  so  suggestive  of  visual  function. 

Differences  observed  in  the  epiphyseal  complex  of  the  various 
species  of  cyclostomes  already  investigated.  Although  all  of  the  three 
European  forms  of  Petromyzon  have  been  carefully  studied  by 
several  investigators,  the  differences  between  them  are  not 
striking.  This  statement  also  applies  to  the  North  American 
form,  Lampetra  wilderi,  described  by  Johnston195  in  1902. 

1.  Petromyzon  planeri.     Ahlborn  ('83) ,2  Beard  ('89), 18  Whit- 
well,  ('88)421  and  Studnicka  ('93) ,384    The  epiphyseal  complex  as 
a  whole  is  not  separated  as  far  from  the  brain  as  in  other  forms, 
due  to  the  fact  that  the  paraphysis  and  dorsal  sac  are  but  little 
developed.     The  parietal  fossa  is  very  shallow  and  is  absent  in 
Ammoccetes  as  is  also  the  white  pigment. 

2.  Petromyzon  fluviatilis.     Ostroumoff  ('87), 291  Owsiannikow, 
('88) ,295  Leydig,  ('96) 239  and  Studnicka  ('99). 388    In  this  form  the 
evagination  of  the  roof  is  very  high  and  the  fossa  in  the  skull  of 
considerable  depth.     The  atrium  contains  a  definite  syncytium 
made  up  of  processes  not  only  from  the  retinal  cells,  but  also 
from  those  situated  in  the  pellucida  as  well. 

3.  Petromyzon   marinus.     Studnicka    ('99). 388     Although  the 
dorsal  sac  is  extremely  high,  the  depression  in  the  skull  is  no 
deeper  than  in  the  case  of  Petromyzon  fluviatilis. 

4.  Petromyzon  wilderi.      Johnston  ('02). 195     In  this  form  the 
stalk  of  the  pineal  organ  has  not  the  significance  as  in  other 
forms,  for  the  pineal  nerve  is  absent  and  the  stalk  contains  no 
nerve  fibers. 

5.  Mordacia    mordax.     Spencer    ('90). 369     In   this  'form   the 
pineal  organ  presents  a  thin,  pigmented  upper  wall  correspond- 
ing to  the  pellucida  of  Petromyzon  and  a  thicker  ventral*  wall  in 
the  form  of  a  retina.     No  definite  statement  is  made  as  to  the 
presence  of  an  atrium,  although  the  lumen  of  the  organ  is  said 
to  be  filled  by  a  coagulum.  There  is  no  evidence  of  any  para- 
pineal  organ,  but  on  the  surface  of  the  head,  midway  between 
the  paired  eyes,  there  is  a  parietal  spot. 


92  FREDERICK    TILNEY   AND    LUTHER   F.    WARREN 

6.  Myxine  gluiinosa  (Bdellostoma).  Kupffer  ('04). 226  In  this 
form  there  is  no  anlage  of  the  epiphysel  complex  whatsoever. 
The  roof  is  entirely  flat,  but  in  spite  of  the  absence  of  the  epi- 
physeal  complex,  both  habenular  ganglia  are  present.  Such 
descriptions  of  the  epiphysis  in  Myxine  as  appear  in  the  litera- 
ture seem  to  be  an  error.  Andrae  Retzius33lA  in  1822  described 
the  pineal  body  in  connection  with  the  habenular  ganglion, 
interpreting  the  latter  to  be  the  epiphysis.  Ley  dig239  in  1896 
believed  that  he  had  found  in  Myxine  the  pineal  body,  but  in 
reality  mistook  a  large  lymph  space  near  the  surface  of  the 
head  for  this  organ.  Studnicka,388  however,  in  his  studies  was 
unable  to  find  any  evidence  of  the  pineal  body  in  Myxine. 

2.  The   comparative   histology    and    anatomy    of    the    epiphyseal 
complex  in  selachians 

Since  the  pineal  organ  is  the  only  part  of  the  epiphyseal  com- 
plex to  make  its  appearance  in  selachians,  the  structure  is  much 
more  simple  than  in  cyclostomes.  Furthermore,  such  parts  of 
the  pineal  organ  as  do  develop  in  selachians  are  relatively  rudi- 
mentary. All  of  the  three  usual  elements  of  the  pineal  organ, 
however,  may  be  identified;  that  is  to  say,  a  hollow  end-vesicle, 
a  stalk,  and  a  proximal  portion.  The  end-vesicle  in  no  instance 
presents  the  two  distinct  walls,  namely,  the  ventral  and  dorsal 
walls  distinguishable  in  cyclostomes,  and  the  end-sac  itself  is 
much  smaller  than  in  the  forms  already  considered.  Slight 
differences  in  the  thickness  of  the  wall  of  the  end-vesicle  may  be 
observed  in  different  places,  but  with  no  great  uniformity.  In 
consequence  of  this  lack  of  differentiation,  there  is  no  evidence 
of  the  formation  of  a  retina,  of  a  pellucida,  or  of  a  white  sub- 
stance, nor  do  any  nerve  fibers  make  their  appearance  in  con- 
nection with  the  end- vesicle.  In  fact,  it  is  a  question  whether 
the  pineal  organ  of  selachians  is  a  primitive  structure  or  one 
that  is  distinctly  retrograde.  In  form  there  may  be  a  consider- 
able difference  in  the  terminal  vesicle;  it  may  be  wedge-shaped, 
cylindrical,  conical,  or  flattened,  but  in  all  instances  it  is  hollow, 
containing  a  lumen,  in  spite  of  the  statement  of  Cattie60  to  the 
contrary  in  his  descriptions  of  Mustelus,  Raia,  and  Acanthias. 


THE    PINEAL   BODY  93 

Frequently  the  wall  of  the  vesicle  presents  reduplication,  as  in 
the  case  of  Spinax  niger  where  there  is  a  distinct  tendency  to 
tabulation,  or  as  in  Acanthias  where  the  folding  of  the  wall 
results  in  the  production  of  two  adjacent  vesicles.  In  a  single 
instance  only  is  there  a  marked  differentiation  between  the 
ventral  and  dorsal  walls.  This  occurs  in  Lamna  cornubica, 
particularly  in  the  embryonic  state,  described  by  Carrington58 
in  1890.  In  this  form  the  under  wall  was  thicker  than  the 
dorsal  wall.  Studnicka389  found  some  tendency  to  such  a  dif- 
ferentiation in  Spinax. 

Hist ologic ally,  the  walls  of  the  end- vesicle  are  made  of  epen- 
dymal  cells,  but  there  are  no  cylindrical  or  spindle  cells  to  be 
observed  in  this  structure.  The  cells  described  in  cyclostomes 
as  having  prolongations  of  such  a  character  as  to  warrant  the 
description  of  ciliated  cells  are  absent  in  selachians  so  that  no 
such  processes  make  their  way  into  the  lumen  of  the  end-vesicle, 
as  is  the  case  in  Petromyzon.  The  nuclei  of  these  cells  are 
situated  at  varying  distances  from  the  surface  of  the  wall  so  that 
the  ependyma  gives  the  impression  of  stratified  epithelium, 
whereas  in  reality  it  is  a  single  layered  epithelial  structure. 
Some  cells  have  a  rather  long  process  which  approach,  but  do 
not  enter,  the  lumen  of  the  end-vesicle.  This  manifestation  is 
taken  as  a  probable  sign  of  an  excretory  function  of  the  cells  in 
question.  Galeotti140  in  1896  described  in  Scyllium  peculiar 
appearances  which  seemed  to  indicate  a  secretory  or  excretory 
activity  on  the  part  the  cells  in  this  portion  of  the  pineal 
organ.  Among  the  more  usual  cells,  according  to  Studnicka,389 
there  are  many  smaller  cells  scattered  here  and  there  of  a  similar 
type  to  the  sense  cells  in  the  retina  of  Petromyzon.  The  signifi- 
cance of  these  cells  is  not  at  all  clear,  and  Studnicka  himself  is 
not  willing  to  accredit  them  with  a  definitely  receptor  function. 

The  stalk  of  the  pineal  organ.  Microscopically,  this  appears  to 
be  a  long,  narrow  strand  connecting  the  end-vesicle  with  the 
roof-plate  of  the  interbrain.  Upon  microscopic  examination 
it  is  found,  however,  to  contain  a  central  but  narrow  lumen,  the 
entire  structure,  therefore,  being  tubular.  In  most  instances 
this  stalk  maintains  an  equal  diameter  throughout  its  entire 


94 


FREDERICK    TILNEY   AND    LUTHER    F.    WARREN 


extent,  although  in  certain  cases  it  becomes  much  attenuated 
as  it  approaches  the  end-vesicle.  A  few  nerve  fibers  course  in 
the  dorsal  wall  of  this  hollow  stalk,  but  these  cannot  properly  be 
considered  the  homologue  of  the  pineal  nerve  in  selachians. 

The  proximal  portion  in  selachians  may  be  readily  made  out. 
As  the  stalk  approaches  the  roof  of  the  interbrain,  it  gradually 
becomes  dilated  and  increased  in  its  transverse  diameter.  Its 
lumen  becomes  larger  and  the  walls  bounding  it  are  thrown  into 
numerous  folds.  Although  the  transition  from  stalk  to  proximal 
portion  is  gradual,  it  is  nevertheless  distinct.  In  a  few  cases 


Fig.  49    End-vesicle  in  the  pineal  organ  of  Acanthias  vulgaris,  according  to 
Studnicka,  1893. 

only,  such,  for  example,  as  Centrophorus,  described  by  Cattie60 
in  1882,  is  there  an  absence  of  this  reduplication  of  the  walls  of 
the  proximal  portion.  As  the  dorsal  wall  of  this  portion  ap- 
proaches the  posterior  commissure  there  appear  in  it  a  few 
strands  of  nerve  fibers  constituting  what  may  be  called  the 
tractus  pinealis.  It  is  doubtful,  however,  whether  the  com- 
missura  habenularis  receives  any  of  the  fibers  which  enter  into 
the  formation  of  this  tract. 

The  sheaths  of  the  pineal  organ  are  the  same  as  those  in  Petro- 
myzon,  namely,  a  membrana  limitans  externa,  a  process  from 


THE    PINEAL    BODY  95 

the  pia  mater  and  another  from  the  dura  mater.  Some  authors, 
.among  them  Cattle,60  have  described  a  parietal  foramen.  In 
Acanthias  vulgar  is  this  opening  in  the  cartilaginous  skull  appears 
to  be  doubled,  the  two  openings  being  separated  by  a  small, 
cartilaginous  bridge.  Neither  Studnicka389  nor  Ehlers108  was  able 
to  discover  any  such  openings  in  the  forms  which  they  investi- 
gated. The  parietal  cornea  is  absent  and  the  parietal  spot  is 
very  infrequently  observed. 

Differences  observed  in  the  epiphyseal  complex  of  the  various 
species  of  selachians  already  investigated. 

ELASMO  BRANCHI 

1.  Scyllium  canicula  and  calulus.     Balfour  (78) 10  studying  the 
embryonic  development;  Owsiannikow  ('88), 295  studying  the  con- 
ditions in  a  65  mm.  embryo;  Cattie  ('82),6°  in  the  adult,  and 
Galeotti  ('96),14°  studying  the  histology.     The  proximal  portion 
in  these  forms  is  not  well  developed  and  the  end- vesicle  is  coni- 
cal.    The  middle   piece  or  stalk  is  cylindrical  in  shape.     The 
structure,  according  to  Galeotti,  shows  stellate  cells  and  epen- 
dymal  cells,  in  addition  to  which,  there  are  certain  cells  which 
are  definitely  fuchsinophile,  which,  according  to  this  observer, 
indicate  secretory  function  because  he  considers  these  granules 
secretory  in  their  nature. 

2.  Acanthias  vulgaris.     Ehlers108  in  1878  and  Cattie  60  in  1882. 
In  this  form  the  proximal  portion  is  thicker  than  the  stalk  and 
both  are  of  unusual  thickness  for  selachians.     The  end-vesicle, 
according  to  Cattie,  is  solid.     Its  walls  show  much  reduplication 
and  the  lumen  is  solidly  filled  with  a  syncytium.     There  is  a 
definite  parietal  foramen. 

3.  Echinorhynus  spinosus.     Jackson  and  Clarke  (75) 193.    The 
pineal  organ  in  this  form  is  a  long,  strand-like  body  extending  far 
over  the  telencephalon  in  the  midsagittal  plane. 

4.  Galeus  canis.     Cattie  ('82). 60    A  conical  end- vesicle  and  a 
conical  proximal  portion  with  a  strand-like  stalk  characterize  the 
pineal  organ  in  this  form.     The  end- vesicle  and  the  stalk  are 
solid  while  the  proximal  portion  retains  its  lumen  and  has,  in 
addition,  many  small  accessory  canuliculae. 


96  FEEDERICK   TILNEY   AND    LUTHER   F.    WARREN 

5.  Mustelus  Icevis.     Cattle   ('82). 60     In  this  form  the  pineal 
organ  is  extremely  simple,  consisting  of  an  end-vesicle,  a  stalk, 
and  a  proximal  portion.     The  end- vesicle  is  flat  and  shows  no 
tendency  toward  reduplication. 

6.  Centrophorus  granulosus.     Cattie  ('82). 60     The  end- vesicle 
in  this  form  has  a  hammer-shaped  appearance.     The  stalk  is 
strand-like  and  the  proximal  portion  conical.     The  pineal  organ 
is   hollow   throughout   its   entire   course.     A   marked   parietal 
depression  lodges  the  structure  and  this  is  surrounded  by  con- 
nective tissue. 

7.  Lamna  cornubica.     Carrington    ('90). 58     This    form    pre- 
sents an  end-vesicle  which  is  conical  and  a  stalk  which  is  cylin- 
drical.    Both  contain  an  irregular  lumen.     The  ventral  wall  of 
the  end- vesicle  is  thicker  than  the  dorsal  wall.     The  cells  in  this 
vesicle  are  for  the  most  part  ependymal,  although  there  are 
many  others  scattered  among  the  cells  of  this  character.     The 
pineal  organ  is  lodged  in  a  depression  surrounded  by  connective 
tissue  and  there  is  a  corresponding  slight  depression  in  the  epi- 
thelium above  the  organ. 

8.  Spinax  niger.     Studnicka  ('93). 384     In  embryos,  larval  and 
adult  forms,  this  species  presents  all  three  portions  of  the  pineal 
organ.     It  is  slender  and  directed  at  right  angles  to  the  roof- 
plate  in  the  embryo,  is  slightly  bent  in  larval  forms,  and  is 
flexed  at  right  angles  in  adults.     The  end- vesicle  is  pressed  into 
a  cartilaginous  skull,  although  there  is  no  actual  parietal  fora- 
men.    The  parietal  portion   consists   of  ependymal   cells   and 
neuroglia  cells.     A  parietal  spot  is  present  in  the  form  of  an 
oval  white  area.     There  is,  however,  no  parietal  cornea. 

9.  Notidanus  griseus.     Studnicka  ('93). 384    The  entire  pineal 
organ  in  this  form  is  sharply  flexed  forward  above  the  forebrain. 
The  proximal  part  is  not  particularly  developed,  but  in  other 
respects  has  the  same  general  form  as  other  species. 

10.  Pristiurus    melanostomus.     d'Erchia    ('96) 109   and   Minot 
('01). 277     Here  the  pineal  organ  extends  directly  forward  in  the 
horizontal  plane  above  the  forebrain  in  the  midsagittal  plane. 
The  end-vesicle  is  much  attenuated  and  the  stalk  is  merely  a 
strand-like  connection  between  the  former  and  the  roof-plate 


THE    PINEAL   BODY 


97 


of  the  interbrain.  There  is  a  small  conical,  proximal  portion. 
Cattie60  states  that  the  parietal  foramen  is  closed  only  by  the 
dura  mater. 

RAIIDAE 

1.  Raia  clavata.  Ehlers  (78)  ;108  Cattie  ('82).6°  In  this  spe- 
cies a  thin,  long  stalk  extends  far  forward  and  terminates  in  a 
definite  end-  vesicle  which  is  enclosed  in  a  deep  prefrontal  fossa. 


/'/"     /'  Os  C/f 


Fig.  50    The  pineal  region  of  Torpedo  ocellata,  according  to  d'Erchia,  1896. 

Hm.,  hemisphere;  Pf  ,  paraphysis;  V.,  velum  transver  um;  Ds.,  dorsal  sac; 
•Ch.,  commissura  habenularis ;  S  h  ,  pars  intercalaris  posterior;  Cp.,  posterior  com- 
missure; M.,  midbrain 

2.  Raia  follonica.     Studnicka  ('95). 385     The  pineal  organ  here 
is  found  as  a  thick  stalk  with  a  lumen.     There  is  no  special 
proximal  portion.     In  the  lumen  there  is  a  syncytium. 

3.  Myliobatis    aquila.     Studnicka  ('95). 385     In  this  form,  as 
in  Raia  clavata,  the  stalk  is  tubular  and  reaches  from  the  inter- 
brain  to  the  roof  of  the  skull.     The  end-vesicle  is  dorsoventrally 
flattened  and  rests  in  the  region  of  the  prefrontal  fossa,  which 
latter  shows  but  a  slight  deepening  in  the  skull. 

4.  Torpedo  marmorata.     Studnicka  ('95). 385     In  this  form  the 
pineal  organ  fails  to  appear,  although  there  are  present  two 
well-developed  ganglia  habenulae. 


MEMOIR   NO. 


98  FREDERICK    TILNEY   AND    LUTHER    F.    WARREN 

5.  Torpedo  ocellala.  d'Erchia  ('96). 109  No  evidence  of  de- 
velopmental differentiation  into  a  pineal  organ  was  found  in 
the  early  stages  of  this  form.  A  well-developed  paraphysis, 
however,  is  present. 

HOLOCEPHALI 

1.  Callorhynchus.    Parker  and  Haswell  ('97). 302 

2.  Chimaera  monstrosa.     Studnicka  ('96). 386     In  both  of  these 
forms   there   is    a   well-defined   epiphysis   and    a    large    dorsal 
sac.     The  pineal  organ  has  a  form  similar  to  other  selachians; 
that  is  to  say,  a  fairly  well-marked  proximal  portion,  a  long, 
slender  stalk  extending  forward  and  expanding  slightly  to  form 
an  end-vesicle  at  its  extremity. 

In  all,  seventeen  species  of  selachians  have  been  examined; 
that  is,  ten  Elasmobranchs,  five  Rays,  and  two  Holocephali. 
In  two  species  a  complete  absence  of  the  pineal  organ  is  reported, 
namely,  Torpedo  ocellata  and  Torpedo  marmorata.  All  of  the 
other  species  present  a  pineal  organ  more  or  less  well  developed. 
In  one  form,  that  is,  Galeus  cam's,  histological  evidence  has  been 
presented  showing  that  there  is  some  reason  to  believe  that  a 
secretory  function  obtains  in  the  pineal  organ  of  this  form. 
Wherever  mention  is  made  of  the  paraphysis  it  seems  to  be  an 
organ  of  considerable  size. 

3.  Comparative  anatomy  and  histology  of  the  epiphyseal  complex 

in  ganoids 

In  all  the  species  of  Ganoids  there  develops  a  fairly  well- 
marked  pineal  organ.  In  one  form  only,  namely,  Amia,  is  there 
any  indication  of  the  presence  of  a  parapineal  organ.  Stannius,373 
giving  the  first  description  of  the  structure  of  the  parapineal 
organ  in  Acipenser  sturio  in  1854,  states  that  the  structure  is  a 
wide  evagination  extending  from  the  roof  of  the  interbrain  and 
connected  with  the  commissura  habenularis.  It  reaches  for- 
ward to  a  fossa  in  the  roof  of  the  skull.  Cattie60  in  1882,  also  in 
Acipenser  sturio,  and  Goronowitsch153  in  1888,  on  Acipenser 
ruthenus,  gave  similar  descriptions  of  the  pineal  organ.  Gar- 
man143  in  1896  and  Johnston194  in  1901  by  means  of  the  Golgi 


THE    PINEAL    BODY 


99 


method  described  the  structure  in  Acipenser  rubicundus.  Both 
observers  were  able  to  differentiate  a  saccular  proximal  portion 
resembling  the  recessus  pinealis,  a  thin,  dorsoventrally  extend- 
ing stalk,  the  latter  producing  a  groove  in  the  dorsal  surface 
of  the  dorsal  sac,  and  finally  an  end-vesicle  greatly  dilated. 
The  end-vesicle  was  of  considerable  size  and  contained  a  well- 
marked  cavity. 

Its  walls  showed  no  tendency  to  differentiation  into  a  dorsal 
pellucidal  layer  or  a  ventral  retinal  layer.  According  to  Stud- 
nicka,386  the  entire  end- vesicle  consists  of  rather  long  cylindrical 


Hm 


Opt 


Fig.  51     The  pineal  region  in  Polyodon  folium,  according  to  Garman,  1896. 
Olf.,  olfactory  lobe;  Opt.,  optic  nerve;  Hm.,  hemisphere;  Po.,  pineal  organ; 
St.,  stalk. 

cells  with  a  generally  oval  nucleus  and  two  processes,  one  a 
slender  extension  reaching  in  toward  the  lumen  of  the  pineal 
organ  and  the  other  a  more  diffuse  ending,  extending  toward 
the  ectal  surface  of  the  wall.  Scattered  here  and  there  among 
these  cells,  which  are  in  the  majority,  are  a  number  of  large 
elements  more  distinctly  oval  in  character  with  a  rounded 
nucleus  situated  near  the  center.  Some  smaller  elements  are 
also  found  scattered  more  numerously  among  both  types  of 
cells.  Studnicka  describes  them,  first,  as  ependymal  cells; 
second,  as  sense  cells,  a  larger-sized  cell  which  he  thinks  may 


100  FREDERICK    TILNEY   AND    LUTHER    F.    WARREN 

be  ganglionic  cells,  and,  third,  neuroglia  cells  which  are  smaller 
and  generally  more  deeply  situated  elements  in  the  walls  of  the 
end-vesicle.  The  stalk  is  strand-like  in  appearance  and  may 


*  b 

Fig.  52    a,  Pineal  organ  in  Acipenser  rubicundus.     b,  Pineal  organ  in  Polyo- 
don  folium. 

contain  a  lumen  in  part  of  its  extent  or  else  running  the  entire 
length  from  the  roof-plate  end-vesicle.  Its  walls  are  made  up 
of  small  neuroglia  cells,  while  in  the  more  dorsal  of  the  two  walls 


THE    PINEAL   BODY 


101 


Johnston194  found  a  number  of  nerve  fibers  constituting  a  layer 
which  extends  from  the  proximal  portion  to  the  commissura 
habenularis,  where  it  apparently  undergoes  decussation  form- 
ing the  so-called  decussatio  epiphysis.  These  observations  were 
made  by  means  of  the  Golgi  method.  Other  fibers  end  freely 
between  the  cells  of  the  stalk.  These  cells,  Johnston  thinks,  are 
rudimentary  or  degenerated  nuclei,  perhaps  related  to  the  pineal 


Fig.  53    Histological  structure  of  the  wall  of  the  pineal  organ  in  Acipensei 
sturio,  according  to  Studnicka.  1893. 

eye.  He  found  a  third  type  of  fibers  in  a  decussation  which 
comes  into  relation  with  the  ganglia  habenulae.  Herrick177  in 
1891  also  mentioned  such  fibers  in  Acipenser.  The  proximal 
portion  consists,  in  the  main,  of  small  neuroglia  elements  with 
some  nerve  fibers  running  in  it,  as  already  described.  Stud- 
nicka386 does  not  think  that  there  is  any  indication  of  a  glandular 
activity  in  this  part  of  the  pineal  organ  which  is  in  any  way 
comparable  to  that  of  the  proximal  portion  in  the  pineal  organ 
of  selachians. 


102  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

Differences  observed  in  the  epiphyseal  complex  in  the  various 
species  of  ganoids  already  investigated 

1.  Acipenser  sturio,  ruthenus,  and  rubicundus.     Cattle  ('82), 60 
Goronowitsch  ('88) ;153  Garman    ('96), 143  and  Johnston    ('01). 194 
The  conditions  in  these  forms  have  been  described  above. 

2.  Lepidosteus    osseus.     Balfour     and     Parker     ('82). 12     The 
pineal  organ  in  this  form  was  first  mentioned  by  these  authors 
and  later  by  Sorensen363  in  1894,  who  described  the  structure  as 
having  a  distinctly  saccular  form. 

3.  Amia    calm.     Goronowitsch     ('88) 153    and    Gage    ('93). 135 
Both  of  these  authors  showed  that  the  pineal  organ  was  a  simple 
sac  in  this  species.     Hill180  in  1894  found  in  the  embryonic  stages 
evidences  of  both  parietal  organs,  namely,   what  he  calls  the 
anterior  epiphysis  and  the  posterior  epiphysis  which  probably 
corresponded  to  the  parapineal  and  pineal  organs  in  Petromyzon, 
while  the  anterior  epiphysis  is  considered  the  homologue  of  the 
parietal  eye  in  Saurians.     In  the  later  embryonic  stages  the 
connection  with  the  brain  of  the  anterior  sac  is  lost.     Finally 
the  pineal  organ  is  pushed  to  the  left  side.     Eycleshymer112 
found  that  the  anterior  organ  has  a  lumen  as  late  as  the  15  to 
16  mm.   embryo.     Nerve  fibers  were  observed  as  late  as   the 
12  to  13  mm.  embryo  going  from  the  commissura  habenularis  to 
the  interior  of  .the  anterior  organ.     Kingsbury205  in  1897  observed 
both  the  pineal  and  parapineal  organs  in  the  adult  Amia.     The 
anterior  organ  was  lying  to  the  left  of  the  pineal  stalk  and  was 
connected  with  the   left    habenular   ganglion  by  means  of  a 
thick,  neural  fasciculus. 

4.  Polyodon  folium.     Garman  ('96). 143     This  species  possessed 
processes   which   look   like   nerve    fibers.     These  processes   go 
from  the  interbrain  roof  and  extend  out  to  an  end-sac  deeply 
situated  in  a  parietal  fossa  of  the  skull.     In  one  case  only  was 
there  a  complete  parietal  foramen. 

5.  Polypterus  bichir.     Waldschmidt  ('87) 412 

6.  Polypterus    senegalus.     Waldschmidt.412      Both     of    these 
species  of  Crossopterygii  present  a  pineal  organ  which  has  a 
tubular  stalk  and  rises  above  the  dorsal  sac,  first  upward,  then 
turns  sharply  forward  to  end  in  a  slightly  dilated  end-vesicle. 


THE    PINEAL   BODY  103 

The  walls  of  the  organ  have,  in  addition  to  the  usual  ependymal 
cells,  some  special  sensory  cells.  In  the  lumen  are  free  cells  with 
no  particular  syncytial  formation. 

In  the  ganoids  no  mention  is  made  of  any  evidence  indicative 
of  glandular  activity.  Six  ganoids  in  all  have  been  carefully 
studied  and  in  only  one,  as  already  stated,  are  there  signs  of  the 
parapineal  organ,  namely,  in  Amia,  otherwise  all  species  present 
a  pineal  organ  which  is  not  as  well  developed  as  in  the  selachians. 

4.  Comparative  anatomy  and  histology  of  the  epiphyseal  complex 

in   teleosts 

The  epiphyseal  complex  in  teleosts  differs  from  that  in  selach- 
ians and  ganoids  in  its  greater  size.  In  some  forms,  however, 
it  is  only  rudimentary,  being  but  a  solid  bud,  while  in  others, 
it  is  a  complicated  end-sac.  It  is  never  in  any  case  like  an  eye 
and  seldom  does  it  come  into  relation  with  the  surface  of  the 
head  as  in  the  cyclostomes.  The  number  of  species  already 
examined  is  perhaps  too  limited  to  make  certain  of  all  of  these 
observations.  The  only  part  of  the  epiphyseal  complex  which 
develops  and  appears  in  the  adult  is  the  pineal  organ.  In  a  few 
instances,  during  the  very  early  stages  of  development,  there 
is  present  what  may  be  considered  the  anlage  of  the  parapineal 
organ.  The  parts  which  the  pineal  organ  presents  in  teleosts 
are  an  end-vesicle,  a  stalk,  and  an  ill-defined  proximal  portion. 
In  many  instances  the  stalk  is  short  and  the  end-sac  large.  In 
most  species  the  end- vesicle  is  pear-shaped  and  connected  with 
the  roof  by  a  hollow  stalk.  The  walls  of  the  end- vesicle  are 
either  flat  or  formed  into  many  folds,  thus  producing  lateral 
diverticula  and  giving  the  sac  the  appearance  of  a  tubular  gland. 
In  some  cases  the  end-vesicle  does  not  develop  as  such,  the  pineal 
organ  being  a  broad  sac  connected  with  the  brain  by  a  slightly 
constricted  area.  The  entire  pineal  organ  may  be  a  rudiment 
as  in  Syngnathus,  where  it  is  almost  solid  throughout  its  entire 
extent.  The  vast  majority  of  the  cells  in  the  end- vesicle  are 
small  and  set  closely  together.  Some  cells  have  an  epithelial 
arrangement:  these  are  doubtless  neui;oglia.  The  presence  cf 


104 


FREDERICK    TILNEY    AND    LUTHER   F.    WARREN 


actual  ganglionic  cells  is  doubtful.  Some  cells  observed  by- 
Hill180  in  1894  have  very  long  processes.  Studnicka386  observed 
that  whatever  the  character  of  the  cells  of  the  end-vesicle  may 
be,  whether  special  sensory  or  not,  the  entire  organ  is  not  a 
gland.  By  this  he  does  not  deny  the  possibility  that  the  struc- 
ture may  be  in  part  glandular.  Galeotti140  in  1896  found  some 


...-Epid 


Cor 


St. 


Pig.  54    The  epiphyseal  complex  in  Anguilla  fluviatilis,  according  to  Leydig, 
1896. 

V.,  velum  transversum;  Ds.,  dorsal  sac;  Po.,  pineal  organ;  St.,  stalk. 

evidence  of. secretory  activity  in  the  cells  of  the  pineal  organ  in 
these  forms.  In  Leuciscus,  he  observed  nuclei  which  had  fuch- 
sinophile  granules  and  also  nucleoli  which  later  appeared  in  the 
protoplasm.  The  product  of  this  secretion  was,  in  his  opinion, 
delivered  to  the  lumen  of  the  end-vesicle  which  is  completely 
surrounded  by  blood  vessels.  The  stalk,  when  definitely  pres- 


THE    PINEAL    BODY 


105 


ent,  has  a  form  similar  in  character  to  the  end-sac  and  is  made 
up,  in  the  main,  of  small  neuroglia  cells.  Nerve  fibers  constitut- 
ing what  has  been  called  the  pineal  nerve  of  the  stalk  have  been 
observed  making  their  way  to  the  posterior  commissure.  Hill180 
observed  in  Salmo  purpuratus,  and  Studnicka386  in  Cyprinus 
carpio,  Carassius  auraius,  Esox  lucius,  and  Cobitis  fossilis 
what  may  be  termed  a  tractus  pinealis  running  from  the  pos- 
terior commissure  through  the  pars  intercalaris  posterior  to  the 


Epid 


At 


Cp 


Ds       Ch 


Sch 


Fig.  55    The  epiphyseal  complex  in  Salmo  purpuratus,  according  to  Hill,  1894. 

V.,  velum  transversum;  Ds.,  dorsal  sac;  Ch.,  commissura  habenularis;  R. 
proximal  portion;  Po.,  pineal  organ;  Tp.,  tractus  pinealis;  Sch.,  pars  intercalaris 
posterior;  Cp.,  posterior  commissure. 

stalk  and  then  in  the  dorsal  wall  of  the  stalk  to  the  end- vesicle. 
Hill  says  these  fibers  are  connected  with  elements  in  the  latter 
vesicle. 

With  reference  to  the  site  and  relation  of  the  pineal  organ  to 
the  skull,  it  has  infrequently  been  observed  that  this  organ 
occupies  a  prefrontal  fossa.  What  has  been  designated  a 
cornea,  namely,  a  large  mass  of  fiberless  connective  tissue  above 
the  end-vesicle,  has  been  described  in  teleosts,  but  there  is  no 
parietal  spot  in  any  other  form  thus  far  investigated. 


106  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

Differences  observed  in  the  epiphyseal  complex  in  the  various 
species  of  teleosts  already  investigated 

PHYSOSTOMI 

1.  Esox  lucius.     Gottsche  ('35) 154  mentioned  for  the  first  time 
the  pineal  organ  in  this  form.     Stieda378  in  1873  called  it  a  red 
body  of  very  insignificant  size.     Cattie60  in  1882  distinguished 
an   end-vesicle  and  a   stalk,  the  former   richly    supplied   with 
blood  and  deeply  sunken  into  a  fossa  in  the  roof  of  the  skull. 
He  described   oval  ependymal   cells,  and   pear-shaped  cells  in 
the  end-vesicle.     The  stalk  was  hollow  and  its  dorsal  wall  con- 
tained a  tractus  pinealis.     There  were  many  folds  in  the  end- 
vesicle. 

2.  Tinea  vulgaris.     Cattie   ('82). 60     In    this  form  there  is  a 
well-defined  proximal  portion,  which,  however,  is  a  fine  strand- 
like  structure.     The  end-vesicle  is  flattened  and  much  expanded. 

3.  Salmo   solar.     Cattie    ('82). 60     This   species   has   an   end- 
vesicle  which  is  pear-shaped  and  a  very  short,  highly  vascular 
stalk.     The  end-vesicle  is  in  contact  with  the  roof  of  the  skull. 

4.  Salmo   fario,   purpuratus  and  fontinalis.     Rabl-Riickhard 
('83) ;319  Hill  ('94).18°     These  forms  present  a  pineal  organ  hav- 
ing an  end-vesicle  in  a  depression  of  the  skull  and  a  stalk  con- 
necting it  with  the  posterior  commissure.     The  stalk  has  a  cen- 
tral canal,  the  lumen  of  which  is  bounded  by  cylindrical  cells. 
Hill  found  in  embryos  not  only  the  pineal  organ,  but  the  para- 
pineal   organ   as   well;   the   latter  remains   rudimentary.     Hill 
called  the  pineal  organ  the  posterior  epiphysis.     It  presents  a 
proximal,  narrow   portion   and   a   distal,    flattened   end-vesicle 
which  is  thick  and  lodged  in  a  deep  fossa  of  the  skull.     It  has 
many  diverticula  and  is  rich  in  blood  vessels.     A  long  canal 
runs  through  the  stalk;  nerve  fibers  connecting  with  some  of 
these  cells  in  the  end-vesicle  make  their  way  through  a  portion 
of  the  stalk,  and  a  definite  tractus  pinealis  in  the  dorsal  wall  of 
the  stalk  ends  in  the  posterior  commissure.     In  the  adult  of  two 
years  old,  Hill  described  a  distal  end-sac  which  retains  the  em- 
bryonic form.     The  rest  disappears.     In  the  distal  part  of  the 
sac  are  many  cell  groups  containing  granular  or  colloid  masses 


THE    PINEAL    BODY  107 

in  irregular  acini.     The  tractus  pinealis  persists.     The  anterior 
epiphysis  in  the  adult  is  reduced  to  a  small  mass  of  cells. 

5.  Anguilla  fluviatilis.     Cattie   ('82) .60     In  this  species  there 
is  a  proximal  portion  and  a  cylindrical  end-sac.     Ley  dig239  in 
1896  described  the  end- vesicle  as  very  much  reduplicated  and 
highly  vascular.     Galeotti140  in  1896  saw  a  clear  caryoplasm  and 
no  granules  or  nucleoli  in  the  end-vesicle.     He,  therefore,  con- 
cludes that  there  is  no  evidence  of  secretory  activity  in  this 
form. 

6.  Clupea  alosa.     Cattie  ('82). 60    A  strand-like  stalk  and  an 
expanded  end-vesicle  are  observed  in  this  form  both  of  which 
are  solid. 

7.  Clupea  harengus.     Holt  ('91).189     In  the  late  larval  stages, 
the  epiphysis  in  this  species  is  a  solid  body.     In  younger  em- 
bryos a  nerve  bundle  extends  from  the  pars  intercalaris  up  the 
stalk.     In  the  later  stages  there  is  a  saccular  epiphysis  with  a 
wide  lumen  three  or  four  cells  deep.     The  lumen  is  filled  with  a 
coagulum.     The  tractus  pinealis  is  present  in  the  dorsal  wall  of 
the  stalk. 

8.  Leuciscus  rutilus.     Rabl-Ruckhard  ('83).319     The  distal  end 
of  the  organ  in   this  form  is  flattened  out  against  the  inner 
surface  of  the  skull.     There  is  a  very  thin  but  long  stalk  (fig.  56). 

9.  Leuciscus  cephalus.     Galeotti  ('96)14°  found  in  the  cells  of 
the  pineal  organ  those  above-mentioned  structural  peculiarities, 
which  he  considered  indications  of  secretory  activity. 

10.  Amiurus  catus.     Ramsay    Wright   ('84).43°     The    pineal 
organ  in  this  species  is  tubular  and  has  the  same  thickness 
throughout  its  entire  extent.     It  ends  in  a  fatty  tissue.     Its 
end-vesicle  does  not  reach  the  cranial  roof.     Its  walls  are  thin 
and  form  no  folds. 

11.  Callichthys  asper  and  litioralis.     Dean   ('88). 81     In  both 
of  these -forms  there  is  a  parietal  foramen  with  a  retinoid  tissue 
lying  beneath  it.     Klinckowstroem208  in  1893  found  a  parietal 
foramen  closed  by  connective  tissue  in  these  forms.     An  end- 
vesicle  was  located  here,  but  showed  no  particular  specialization. 

12.  Doras,  Clarias,  Loricaria.     Dean  ('88). 81     In  these  species 
there  is  a  parietal  foramen. 


108 


FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 


13.  Coregonus  albus.     Hill  ('91). 179     In  the  embryonic  state 
of  this  species  the  anlagen  of  the  pineal  and  parapineal  organs 
both  occur. 

14.  Caioslomus  teres.     Hill  ('94)18°  found  the  anlagen  of  the 
anterior  and  posterior  epiphysis  in  embryos  of  this  form.     These 
were  almost  transversely  placed  in  relation  to  each  other. 


Front 


Hm 


Fig.  56    Transverse  section  through  the  end-vesicl'e  of  the  pineal  organ  in  Leu- 
ciscus  rutilus,  according  to  Rabl-Riickhard,  1883. 
Po.,  pineal  organ;  Hm.,  hemispheres. 

15.  Cobitis  fossilis  and  barbatula.  Studnicka  ('96). 386  The 
pineal  organ  in  these  species  is  tubular.  The  distal  end  forms  a 
large  sac  which  lies  beneath  the  skull.  The  tractus  pinealis  is 
present. 


THE    PINEAL   BODY 


109 


16.  Belone  acus.     Studnicka  ('96). 383     In  this  species  there  is 
a  long,  tubular  stalk.     Ependymal  cells  form  the  walls  of  this 
stalk  and  have  an  arrangement  reminiscent  of  the  retinal  sen- 
sory cells  of  the  retina  of  Petromyzon  especially  of  the  region  of 
the  large  end- vesicle  (fig.  57). 

17.  Cyprinus    carpio.     Studnicka    ('96). 383     The    end-vesicle 
in  this  form  is  a  circumscribed  dilatation  and  has  a  thin,  hollow 


Cr 


Hn 


Ch 


Fig.  57    The  epiphyseal  complex  in  Belone  acus,  according  to  Studnicka,  1896. 

Ls.,  lamina  terminalis;  Pf.,  paraphysis;  D.,  dorsal  sac;  Ch.,  commissura  ha- 
benularis;  R.,  proximal  portion;  Po.,  pineal  organ;  Cp.,  posterior  commissure; 
M.,  midbrain. 

stalk,  in  the  dorsal  wall  of  which   there   courses   the   tractus 
pinealis. 

18.  Carassius  auratus.     Studnicka  ('96). 386    The  pineal  organ 
in  this  form  is  tubular  throughout  its  entire  extent.     There  is  a 
tractus  pinealis  as  usual  in  the  stalk,  but  no  fossa  in  the  skull. 

19.  Argyropelecus    hemigymnus.     Handrick    ('01). 168     In    the 
adult  of  this  form  both  the  pineal  and  parapineal  organs  appear 
to  be  present.     The  pineal  organ  has  a  thin  stalk  and  a  large 


110 


FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 


end-vesicle  which  is  much  folded  and  highly  vascular,  being 
mushroom  in  shape.  This  sac  has  much  to  suggest  glandular 
activity.  No  tractus  pinealis  could  be  discovered  in  the  stalk. 
The  end-vesicle  lies  beneath  the  roof  in  the  frontal  region  and 
there  is  in  this  particular  area  an  actual  frontal  or  parietal  fora- 
men. The  parapineal  organ  is  tubular  in  form  and  lies  in  front 


Fig.  58    Cross  section  of  pineal  organ  and  dorsal  sac  in  Argyropelecus  hemigym- 
nus,  according  to  Handrick,  1901. 
Ds.,  dorsal  sac;  Po.,  pineal  organ. 

of  the  pineal  organ.  It  is  shorter  than  the  pineal  organ  and  does 
not  reach  the  parietal  foramen.  It  has  a  long  stalk.  Stud- 
nicka386  thinks  Handrick' s  parapineal  organ  is  nothing  more  than 
a  peculiar  formation  of  the  dorsal  sac. 

20.  Opsanus.     Terry  ('II).392     The  pineal  organ  in  this  species 
presents  an  oval  end-vesicle  with  a  long  slender  stalk,  both  of 


THE    PINEAL    BODY  111 

which  contain  a  lumen,  but  neither  have  connection  with  the 
third  ventricle.  The  cavity  of  the  pineal  organ  is  traversed  by 
protoplasmic  processes  forming  a  dense  meshwork  from  wall  to 
wall.  Although  the  pineal  organ  is  highly  vascular  in  Opsanus, 
it  does  not  conform  in  structure  to  any  of  the  known  ductless 
glands,  and  is,  therefore,  probably  not  glandular.  There  is  no 
pineal  nerve,  no  parietal  foramen  or  fossa,  no  dorsal  sac  or 
paraphysis. 


PV 


D 
PC  Y 

Fig.  59     Pineal  region  in  an  embryo  of  Opsanus,  according  to  Terry,  1911. 

T.R.,  lamina  terminalis;  P.,  paraphysis;  V.,  velum  transversum ;  P.V.,  post- 
velar  arch  (dorsal  sac);  S.,  commissura  habenularis;  E.,  epiphysis;  P.O.,  pos- 
terior commissure. 

PHYSOCLYSTI 

21.  Gadus  morrhua.     Baudelot   (70). 14     The  pineal  organ  in 
this  species  is  a  long,  pear-shaped  structure.     Cattie60  in  1882 
distinguishes  a  strand-like  proximal  portion  and  an  end-vesicle 
rich  in  blood  vessels.     In  the  latter  are  round  and  oval  nuclei 
and  round  and  pear-shaped  cells  with  one  or  two  processes. 

22.  Trigla  hirundo.     Ussow    ('82).40;     A   short  pineal  organ 
with  a  hollow  end-stalk  is  the  characteristic  in  this    species. 
The  end-vesicle  is  convoluted  and  reminiscent  of  the  conditions 
in  the  hypophysis.     The  cells  bordering  upon  the  lumen  are 
ciliated  while  the  parenchymal  cells  are  probably  neuroglia. 


112  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

23.  Cyclopterus  lumpus.     Cattle    ('82). 60     In   this   form    the 
pineal  organ  is  only  rudimentary,  being  made  up  of  a  short, 
conical  body  representing  the  stalk,   while  the  distal  part  is 
entirely  absent. 

24.  Lota   vulgaris.     Cattie   ('82). 60     As    in    Gadus,   the  end- 
vesicle  in  this  species  lies  against  the  roof  of  the  skull.     The  cells 
in  this  vesicle  are  similar  to  those  in  Gadus. 

25.  Pleuronectes  platessa.     Cattie  ('82). 60     In  this  species  the 
stalk  is  solid  and  so  also  is  the  end- vesicle.     The  latter  is  highly 
vascular  and  the  stalk  is  very  long. 

26.  Lucioperca    vitrea.     Hill    ('94).18°     In    this    species    the 
anlagen  of  both  the  parapineal  organ  and  the  pineal  organ 
appear. 

27.  Lophius  piscatorius.     Studnicka  ('96). 386    An  end- vesicle 
and  a  stalk  are  present  in  this  form.     The  end-vesicle  is  in  a 
deep  fossa.     There  are  two  types  of  cells  in  it  besides  the  epen- 
dymal  layer,  namely,  neuroglia  cells  and  sensory  cells.     Nerve 
fibers  were  observed  in  the  stalk. 

28.  Cepola  rubescens.     Studnicka  ('96). 386    A  thin  stalk  with 
an  expanded  end-vesicle  sharply  flexed  forward  is  the  charac- 
teristic in  this  species.     The  lumen  in  both  is  conspicuous.     The 
end- vesicle  is  much  convoluted  and  rests  against  the  roof  of 
the  skull. 

29.  Anarrhichas    lupus.     Studnicka    ('96). 386     In    this    form 
there  is  a  very  long  stalk,  but  no  recognizable  end- vesicle.     There 
is  a  tractus  pinealis  in  the  dorsal  wall  of  the  stalk  and  a  plasmatic 
lens  in  its  lumen. 

30.  Ophidium  barbatum.     Studnicka  ('96). 386     In  this  species 
there  is  a  thin,  long,  hollow  stalk  and  a  very  small  but  elongated 
end-vesicle.     There  is  no  fossa   in   the   skull   and   no  tractus 
pinealis,  but  many  blood  vessels  accompany  the  stalk  as  far  as 
the  end-vesicle. 

31.  Arnoglossus  lanterna.     Studnicka  ('96).386     In  this  species 
there  is  a  hollow  and  long  stalk  with  a  well-marked  end-vesicle. 
This  vesicle  is  vascular,  but  is  situated  in  a  position  far  removed 
from  the  skull  roof. 


THE    PINEAL   BODY  113 

LOPHOBRANCHII 

32.  Syngnathus  acus.     Studnicka   ('96). 386    The  pineal  organ 
in  this  species  is  rudimentary,  only  the  proximal  portion  of  it 
being  present.     In  this  there  is  a  small  lumen. 

33.  Hippocampus  spinosus.     Studnicka  ('96). 386    The  pineal 
organ  in  this  form  is  a  small,  short  sprout,  the  distal  end  of  which 
does  not  reach  the  roof. 

In  all,  thirty-three  species  of  teleosts  have  been  investigated. 
Of  these,  thirty  species  present  a  more  or  less  well-developed 
pineal  organ.  In  one  form  it  is  almost  entirely  absent  present- 
ing itself  only  as  an  inconspicuous  rudiment.  This  is  the  case 
in  Syngnathus  acus.  In  a  second  instance,  Hippocampus 
spinosus,  the  pineal  organ  is  little  more  than  a  short  sprout.  In 
five  instances  among  the  teleosts  both  pineal  and  parapineal 
organs  appear,  the  latter  occurring  either  in  the  adult,  which 
is  rare,  or  during  the  earlier  stages  of  development.  Both 
organs  appear  in  the  anlagen  in  Coregonus  albus,  Lucioperca 
vitrea,  and  Catostomus  teres,  but  later  disappear  in  these  forms. 
Both  organs  are  well  marked  in  anlagen  and  remain  as  discern- 
ible rudiments  in  Salmo  purpuratus  and  fario  and  also  in  Argyro- 
pelecus  hemigymnus.  In  one  instance,  Leuciscus  cephalus, 
there  was  definite  evidence  of  secretory  activity  in  the  pineal 
organ.  In  three  species  there  was  evidence  of  a  retina  in  the 
pineal  organ,  either  because  of  the  presence  of  specialized  sensory 
cells  or  of  nerve  fibers  coming  into  connection  with  these  cells. 
In  three  instances  there  was  a  distinct  parietal  foramen.  It  is 
significant  in  this  connection  to  note  that  in  no  instance  in 
which  there  was  a  retinal-like  structure  or  cellular  formation 
and  arrangement  suggestive  of  a  retina,  did  there  occur  a  parietal 
foramen.  In  seven  cases  the  end- vesicle  of  the  pineal  organ  was 
lodged  in  a  fossa  on  the  under  surface  of  the  skull.  In  seven 
species,  namely,  Cobilis  fossilis  and  barbatula,  Lophius  pisca- 
torius,  Cyprinus  carpio,  Carassius  auratus,  Anarrhichas  lupus, 
Pleuronectes  platessa,  and  Clupea  harengus,  there  is  evidence 
of  a  nervus  pinealis  or  a  tractus  pinealis.  All  of  these  descrip- 
tions except  one  are  given  by  Studnicka.386  This  observer  makes 
the  statement  that  there  is  no  nervus  pinealis  in  Ophidium 
barbatum. 

MEMOIR   NO.    9 


114  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

5.  Comparative  anatomy  and  histology  of  the  epiphyseal  complex 

in  amphibia 

In  amphibia  the  pineal  organ  alone  makes  its  appearance. 
In  no  other  form  is  this  organ  so  little  developed.  It  presents  a 
small  end- vesicle  which  Stieda379  first  recognized  and  described 
as  the  frontal  subcutaneous  gland.  This  end-vesicle  is  attached 
by  means  of  a  thread-like  strand  to  a  considerably  expanded 
proximal  portion,  to  which  latter  the  name  of  epiphysis  or  corpus 
pineale  has  been  ascribed.  The  pineal  organ  consists,  there- 


Fig.  60    Head  of  Rana  temporaria  showing  the  unpaired  pineal  eye,  situated 
between  the  paired  eyes,  according  to  Stieda,  1865. 

fore,  of  the  usual  parts,  namely,  an  end-vesicle,  a  stalk,  and  a 
proximal  portion  which  is  particularly  conspicuous  in  amphibia. 
The  end-vesicle  in  so  far  as  is  known,  is  present  in  all  forms 
except  Hyla  arborea,  the  absence  in  this  form  being  noted  both 
by  deGraaf,155  and  Leydig.238  In  shape,  the  end-vesicle  is  round, 
oval,  or  kidney-shaped.  Stieda379  and  deGraaf155  found  it  solid, 
containing  a  lumen  only  in  Bombinator.  According  to  Stieda, 
its  diameters  are  from  .12  to  .15  mm.  deGraaf  found  these 
diameters  in  Rana  esculenla  from  .126  to  .145  mm.,  while 
Lessona241  in  the  forms  studied  by  him  found  that  the  diameter 
was  less  than  1  mm.  A  number  of  observers,  including  Ostrou- 
moff291  ('87) ;  Leydig238  ('91) ;  Galeotti140  ('96),  and  Braem39  ('98), 


THE    PINEAL   BODY 


115 


maintain  that  the  frontal  organ  contains  a  cavity.  According 
to  Leydig,  this  organ  contains  pigment  in  Bombinator,  but 
otherwise,  in  frogs,  the  cells  are  pigment-free.  Histologically, 
the  cellular  elements  of  the  frontal  organ  show  no  definite 
arrangement.  These  cells  are  usually  long  and  their  mass 
is  traversed  by  a  few  isolated  fibers.  deGraaf  and  Leydig  both 
found  evidence  of  fatty  degeneration  in  the  organ.  The  so- 
called  frontal  subcutaneous  gland  of  Stieda  is  situated,  as  de- 
scribed by  that  author,  directly  under  the  corium  of  the  skin 


Epid 


M 


Pf  V  Ds        Ch 

Fig.  61  The  epiphyseal  complex  in  the  pineal  region  of  Rana  temporaria,  ac- 
cording to  Braem,  1898. 

Ls.,  lamina  terminalis;  Pf.,  paraphysis;  V.,  velum  transversum;  Ds.,  dorsal 
sac;  Po.,  pineal  organ;  N .pin.,  pineal  nerve;  Ch.,  commissura  habenularis;  Ep.t 
proximal  portion;  Cp.,  posterior  commissure;  M..  midbrain. 

in  the  midline  of  the  head  and  upon  a  transverse  line  from  pupil 
to  pupil.  According  to  Lessona,241  its  position  is  marked  by  a 
clear,  white  spot  on  the  top  of  the  head,  not  well  developed  in 
all  forms,  but  first  described  by  Stieda375  as  the  Scheitelfleck  or 
parietal  spot.  According  to  Leydig,238  this  spot  is  best  made 
out  in  Rana  arvalis  and  agilis.  It  also  occurs  in  Rana  esculenta. 
The  stalk  of  the  pineal  organ  in  amphibia  exists  as  a  thin, 
strand-like  structure.  Stieda375  in  1865  first  referred  to  it  as 
a  thread  connecting  the  frontal  gland  with  the  skull.  Ciaccio65 
in  1867  recognized  the  nerve  fibers  in  this  strand.  Lessona241  in 
1880,  deGraaf155  in  1886,  and  Leydig238  in  1891,  all  observed  the 
nerve  fasciculus  in  older  animals,  but  did  not  appreciate  its 
significance.  They  thought  it  to  be  the  remnant  of  the  connect- 


116  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

ing  strand  between  the  attached  and  detached  parts  of  the 
pineal  organ,  thus  representing  a  degenerative  process.  Braem39 
in  1898  also  found  this  fasciculus  and  made  the  further  observa- 
tion that  it  contained  heavily  myelinized  nerve  fibers.  He 
likewise  was  of  the  opinion  that  there  was  evidence  of  degenera- 
tion in  this  nerve  fasciculus,  in  this  way  confirming  the  view  of 
deGraaf  and  Leydig.  Haller166  in  1898  stated  that  the  fibers  of 
the  tractus  pinealis  spring  from  two  branches  of  roots  connected 
with  the  thalamus  ventromedial  to  the  commissura  posterior. 
Gaupp147  in  1898,  who  first  applied  the  term  of  tractus  pinealis 
to  these  fibers,  observed  fine  nerve  bundles  passing  in  the  ventral 
portion  of  the  epiphyseal  stalk.  Most  observers  believe  that 
these  fibers  come  into  relation  with  the  posterior  commissure. 
The  proximal  portion  of  the  pineal  organ.  This,  as  already 
stated,  was  known  as  the  epiphysis  or  corpus  pineale.  It  was 
also  called  by  Gaupp147  in  1898  the  pediculus  corporis  pinealis. 
Osborn288  in  1884  described  it  as  a  cylindrical,  hollow,  anteriorly 
flexed  sac  whose  lumen  was  in  communication  with  the  third 
ventricle.  Rabl-Rtickhard317  in  1880  states  that  the  proximal 
portion  is  solid.  Osborn,  on  cross  section,  described  it  as 
round.  Gaupp147  and  Braem39  state  that  the  organ  has  an 
elliptical  form  with  many  short  diverticula  which  give  it  a 
glandular  appearance.  In  this  feature  it  is  like  some  teleosts, 
reptiles,  and  birds.  Galeotti140  in  1896  found  evidence  of  secre- 
tory activity  in  Rufo  and  Rana,  for  example,  granules  in  the 
cytoplasm  staining  with  acid  fuchsin.  Studnicka386  in  1896  saw 
the  same  appearances  in  adult  animals  which  he  thought  were 
sensory  cells  and  which  he  likened  to  the  sense  cells  in  the  pineal 
organ  in  Petromyzon.  Ostroumoff291  in  1887  found  fine  fibers 
between  these  cells. 

Differences  observed  in  the  epiphyseal  complex  of  the  various 
species  of  amphibia 

URODELA 

1.  Amblysloma  mexicanum.     Stieda  (75).379     In  this  form  the 
chorioid  plexus  was  first  mistaken  for  the  epiphysis.     Orr286  in 


THE    PINEAL   BODY  117 

1889  first  discovered  the  pineal  organ  in  embryos.  Eycles- 
hymer112  in  1892  made  a  more  extensive  study  of  this  organ  and 
found  the  epiphysis  to  be  a  long,  glove-finger  shaped  struct- 
ure. The  cells  in  the  under  wall  were  somewhat  larger  than 
those  in  the  upper  wall  and  some  of  them  contained  pigment. 

2.  Amphiuma  means.     Osborn  ('83). 287    In  this  species  there 
is  a  marked  plexiform  paraphysis,  while  the  pineal  organ  extends 
forward  as  a  small  sac  over  the  commissura  habenularis. 

3.  Menopoma     alleghaniense.     Osborn    ('84). 288     The    pineal 
organ  in  this  species  is  a  saccular  evagination  with  a  lumen 
opening  into  the  third  ventricle. 

4.  Menobranchus.     Osborn   ('84). 288    In  this  form  the  pineal 
organ  is  a  long,  flattened  sac  completely  detached  from  the 
brain.     Kingsbury204  in  1895  showed  that  there  is  a  well-marked 
paraphysis  and  also  that  there  are  nerve  fibers  in  connection 
with  the  pineal  organ. 

5.  Salamandra    maculosa.     Burckhardt    ('91). 43     The   pineal 
organ  in  this  species  is  a  short,  hollow,  and  rudimentary  stalk. 
There  is  a  flattened  end- vesicle  in  which  there  appears  evidences 
of  degeneration. 

6.  Diemyctylus  viridescens.     Gage  ('93). 135    The  pineal  organ 
in  this  form  is  very  small  in  the  adult  and  there  is  no  lumen  in 
any  portion  of  it,     There  is,  however,  a  well-developed  para- 
physis. 

7.  Desmognathus   fuca.     Fish  ('95). 119     The   pineal  organ  in 
this  species  is  a  small  compressed  structure.     It  contains  no 
lumen  in  the  adult,  but  in  the  larva  the  organ  is  hollow. 

8.  Triton  taeniatus,   cristatus  and  alpeslris.     deGraaf  ('86) 155 
The  pineal  organ  in  these  species  is  rudimentary.     There  is  a 
short,  hollow  stalk  and  a  flattened  end-sac  in  which  there  is 
evidence  of  a  process  of  degeneration.     This  same  form  was 
studied  by  Blanc34  in  1900  with  practically  the  same  results. 

9.  Spelerpes  fuscus.     Galeotti    ('96).14°     In  this   species  the 
pineal  organ  is  oval  and  hollow.     The  end-sac  is  directly  in 
connection  with  the  commissura  habenularis  and  there  is  no 
stalk.     The  cells  have  an  epithelial  arrangement  and  are  formed 
in  alveoli,  giving  the  structure  a  glandular  appearance. 


118  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

10.  Proteus   anguinus.     Galeotti   ('96).14°     The  pineal  organ 
in   this  form  is  small  and  pyriform  and  has  no   evidence  of 
secretory  function. 

11.  Salamandrina    perspicillata.      Galeotti    ('96.140     In    this 
species  the  pineal  organ  is  a  small,  flattened  structure. 

APODA. 

1.  Ichthyophis  gluiinosa.  Burckhardt  ('90). 42  The  pineal  organ 
in  this  form  is  small  and  pyriform  and  has  a  short  stalk,  but 
does  not  reach  the  skull  roof.  A  well-developed  paraphysis  is 
present.  Fibers  from  the  end- vesicle  seem  to  make  their  way  to 
the  commissura  habenularis. 

ANURA 

1.  Rana  esculenta.     Leydig  ('68)  ,233     In  this  species  the  end- 
vesicle  has  a  figure-of-eight  shape  and  is  solid.     Leydig238  later  in 
1891,  could  find  no  evidence  of  a  parietal  spot  in  Rana  fusca. 
deGraaf155  in   1886  found  a  well  marked  end- vesicle  which  was 
solid  and  round  and  a  well-developed  parietal  spot. 

2.  Ceratophrys.     Lessona    ('80). 241     There    is   a   fairly    well- 
marked  end-vesicle  in  this  species. 

3.  Bufo  cinereus.     Lessona  ('80) 241  did   not  observe  a  pineal 
organ  in  this  form,  but  it  was  found  subsequently  by  deGraaf155 
in  1886.     Studnicka386  also  found  it  in  young  larvae. 

4.  Pelobates  fuscus.     Lessona    ('80) 241  found  the   end- vesicle 
in  this  species. 

5.  Discoglossus.     Lessona  ('80). 241     A  fairly  well-marked  end- 
vesicle  exists  in  this  species. 

6.  Alytes  obstetricans.     Lessona    ('80) ,241     In  this  form  there 
is  a  well-marked  end-vesicle  which  was  first  accurately  described 
by  deGraaf.155 

7.  Rana    occipiialis  and  tigrina.     Lessona  ('80). 241     In  these 
forms   the-  pineal    organ   presents   a   well-marked   end-vesicle. 

8.  Pipa  americana.     Lessona   ('80). 241     In  this  species  there 
is  no  end- vesicle. 

9.  Hyla  arborea.     deGraaf  ('86), 15'5  and  Leydig  ('91)238  both 
found  that  the  end-vesicle  was  absent  and  that  the  skin  in  the 
usual  position  of  the  parietal  spot  showed  nothing  of  the  existence 
of  such  a  structure. 


THE    PINEAL   BODY  119 

10.  Bombinator  igneus.  Leydig  ('68)  ;233  deGraaf  ('86). 155  In 
this  species  the  end-vesicle  is  saccular. 

In  the  twenty-two  species  of  amphibia  investigated,  the  great 
majority  present  a  well-developed  paraphysis.  In  but  a  single 
well-defined  instance  is  there  evidence  of  a  tendency  toward  the 
formation  of  a  retina.  This  occurs  in  Amblystoma  mexicanum 
in  which  there  is  evidence  of  pigment  formation  in  some  of  the 
cells  of  the  end-vesicle.  In  several  forms  the  stalk  contained 
fibers  suggestive  of  the  pineal  nerve.  With  reference  to  the 
possible  glandular  character  of  the  organ  it  must  be  borne  in 
mind  that  Stieda's379  original  description  referred  to  the  struc- 
ture as  the  frontal  subcutaneous  gland.  The  general  arrange- 
ment of  the  cells,  both  in  the  end- vesicle  and  i(n  the  proximal 
portion,  has  epithelial  masses  which  tend  to  lend  weight  to  the 
view  that  the  organ  may  have  secretory  function.  In  only  one 
instance,  however,  that  is  in  Spelerpes  fuscus,  has  there  been 
observed  any  definite  evidence  of  glandular  activity  in  the 
pineal  organ. 

6.  Comparative  anatomy  and  histology  of  the  epiphyseal  complex 

in  Reptilia 

In  considering  the  conditions  present  in  the  epiphyseal  com- 
plex of  reptilia,  two  groups  of  these  animals  must  be  distin- 
guished. The  first  group  is  that  comprising  the  more  ancient 
reptiles,  e.g.,  the  saurians  and  also  the  prosaurians  as  represented 
by  Sphenodon.  In  the  second  group  are  the  reptiles  of  more 
recent  history,  including  ophidians,  chelonians  and  crocodilians. 
It  is  in  the  first  group,  however,  that  the  most  striking  appear- 
ances are  observed  in  the  epiphyseal  complex.  In  these  forms 
there  develops  a  structure  so  remarkable  for  the  many  features 
which  identify  it  as  a  visual  organ  that  the  term  parietal  or 
third  eye  by  which  it  has  been  designated  seems  altogether  justi- 
fied. Quite  as  striking  in  a  negative  way,  on  the  other  hand, 
are  the  conditions  in  the  ophidians  and  in  the  chelonians  where 
this  eye  not  only  altogether  fails,  but  there  is  no  evidence 
whatever  of  a  parapineal  organ  either  in  adult  forms  or  in 
the  anlage,  while  the  pineal  organ  also  shows  marked  regressive 


120 


FREDERICK    TILNEY   AND    LUTHER   F.    WARREN 


alterations  in  the  loss  of  several  of  its  parts  as  compared  with  the 
lower  forms  already  considered.  Finally  the  reported  absence 
of  any  epiphyseal  structures  whatsoever  in  crocodilia  offers  much 
room  for  speculation  or,  perhaps,  serves  as  an  incentive  to  rein- 
vest igat  ion. 

The  pineal  organ  in  saurians  and  prosaurians  (form  Sphenodori) 
seldom  presents  all  three  of  the  several  parts  usually  observed 
in  the  pineal  organ,  and  it  is  not  possible  to  identify  an  end- 


Schd 


Fig.  62    The  epiphyseal  complex  in  Sphenodon  according  to  Spencer,  1886. 
Pa.,  parapineal  organ  (end-vesicle);  Pf.,  paraphysis;  Ds.,  dorsal  sac;  Ep., 
fproximal  portion  of  pineal  organ;  M.,  midbrain. 

vesicle,  a  stalk,  or  a  proximal  portion.  Often  the  end- vesicle  is 
absent,  and  in  no  instance  does  it  assume  the  proportions  or 
the  characteristics  of  a  visual  organ.  The  stalk  is  usually 
hollow,  but  contains  no  nerve  fibers,  and  in  the  instances  in  which 
the  end- vesicle  is  absent,  the  stalk  is  drawn  out  into  a  tapering 
process  or  end-tube.  Melchers269  in  1899  showed  that  not  only 
may  the  end-sac  be  absent,  but  the  rest  of  the  parapineal  organ 
may  present  itself  in  a  degenerative  condition.  This  is  true  in 


THE    PINEAL   BODY  121 

Platydactylus.  In  some  cases,  as  in  Gehyra  oceanica  and 
Hemidaclylus  mahouia,  described  by  Stemmler374  in  1900,  the 
entire  epiphyseal  complex  may  be  only  recognized  in  the  slightest 
rudiment  possible.  In  one  instance  reported  by  Studnicka,386 
namely,  Pseudopus  pallasi,  there  is  an  end-vesicle,  a  stalk,  and 
&  proximal  portion.  The  stalk  is,  in  fact,  a  double  one,  or,  in 
other  words,  there  is  a  main  stalk  and  a  secondary  accessory 
connection  between  the  end-vesicle  and  the  roof-plate  of  the 
brain. 

The  proximal  portion  of  the  pineal  organ,  known  as  the  epi- 
physis  or  corpus  pineale,  is  present  in  all  forms.  In  some  cases 
the  proximal  portion  is  a  simple  pyriform  structure  attached  by 
a  thin  stalk  to  the  roof  of  the  interbrain.  In  other  instances  it 
is  spindle-shaped  or  oval.  The  walls  of  the  proximal  portion 
are  thick  and  usually  flat  inside  as  well  as  outside.  In  some 
cases  there  are  inner  reduplications,  as  in  the  fish.  Leydig238 
in  1891  found  thick  accessory  spaces  in  the  organ  of  Lactera 
ocellaia  and  Anguis  fragilis  due  to  septal  formation.  The  wall 
may  be  much  folded,  giving  the  appearance  of  a  complicated 
glandular  structure.  Edinger105  in  1890  showed  this  in  one  of 
his  cuts  (fig.  63). 

The  histological  structure  of  the  pineal  organ.  The  chief  cellular 
constituent  of  the  pineal  organ,  both  in  its  end-vesicle  when 
present  and  in  the  proximal  portion,  is  the  ependymal  cell. 
Neuroglia  cells  also  occur  interspersed  among  the  ependymal 
elements,  but  there  are  no  ganglionic  cells.  Nerve  fibers  lie 
parallel  with  the  outer  dorsal  surface  quite  similar  to  the  nerve 
fibers  in  other  pineal  organs.  These  are  probably  the  nerve 
fibers  which  constitute  the  tractus  pinealis.  Klinckowstroem207 
in  1893  found  cilia  on  the  cells  of  the  pineal  organ  in  embryos 
of  Iguana  and  Tejus,  but  not  in  the  adults  of  these  species. 
Pigmentation  is  either  entirely  absent  in  all  parts  of  the  pineal 
organ  or  when  present  it  is  in  the  interior  of  the  cylindrical 
cells  placed  in  the  lumen.  A  tractus  pinealis  was  described  by 
Leydig239  in  1896  in  Platydactylus.  Melchers,  however,269  in  1899, 
showed  these  fibers  were  probably  connective  tissue.  Saurians, 
.as  a  rule,  although  they  do  not  in  every  case  present  a  well- 


122 


FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 


marked  tractus  pinealis,  nevertheless  in  a  certain  number  of 
instances  a  nerve  tract  may  be  observed  connecting  the  pineal 
organ  with  the  roof  of  the  interbrain. 

In  Ophidia  the  pineal  organ  is  rudimentary.  Only  the  prox- 
imal portion  persists  in  the  snakes.  This,  however,  has  under- 
gone considerable  modification  from  the  proximal  portion  already 
encountered  in  the  lower  vertebrates.  In  the  true  snakes  it  is 
a  compact,  highly  vascular  structure  to  which  the  term  epiphysis 
or  corpus  pineale  may,  in  the  strict  sense,  be  applied.  Hoff- 


Epid 


Pa 


Fig.  63     The  epiphyseal  complex  in  Anguis  fragilis,   according  to  Leydig, 
1891. 

P. a.,  parapineal  organ;  Ep.,  proximal  portion  of  pineal  organ. 

mann186  in  1886  showed  that  the  corpus  pineale  in  ophidia  begins 
in  its  development  as  a  simple  evagination  from  the  interbrain 
roof.  How  it  attains  its  later  complicated,  compact  form  is  not 
yet  exactly  known.  No  doubt  the  solid  epiphysis  due  to  the 
proliferation  of  the  wall  of  the  anlage  causes  the  obliteration  of 
the  lumen  of  the  original  evagination.  A  paraphysis  develops 
early  in  ophidians  and  has  in  its  inception  the  same  general  form 
as  the  epiphysis.  The  pineal  region  in  the  adult  consists,  there- 
fore, of  a  paraphysis  which  is  a  thick-walled  structure  associated 
with  the  chorioid  plexus,  a  velum  transversum  and  a  dorsal  sac 


THE    PINEAL   BODY  123 

also  complicated  in  the  chorioid  plexus,  a  commissura  habenularis, 
an  epiphysis  with  a  fairly  well  marked  recessus  pinealis  and  a 
posterior  commissure.  Herrick177  in  1891  described  the  epi- 
physis in  ophidia  as  a  compact,  somewhat  rounded  or  oval 
body  whose  interior  consists  of  a  connective  tissue  network  with 
many  blood  vessels,  thus  giving  it  the  appearance  of  a  branched, 
tubular  gland.  Studnicka386  maintains  that  nothing  definite  is 
known  of  the  significance  of  the  epiphysis  in  snakes.  Its  un- 
usually rich  capillary  blood  supply  speaks  in  favor  of  the  sup- 
position that  the  organ  is  a  gland  which  contributes  its  product 
to  the  blood  stream. 

In  Chelonia  the  pineal  organ  is  only  in  a  rudimentary  condi- 
tion and  develops  in  these  forms  an  epiphysis  or  corpus  pineale. 
Just  as  in  ophidians,  the  end-vesicle  and  the  stalk  of  the  pineal 
organ  appear  not  to  be  laid  down  in  anlage,  or  if  it  does  occur  in 
the  early  stages  of  the  development,  it  soon  disappears,  leaving 
only  the  proximal  portion  to  represent  the  pineal  organ  in  these 
forms.  Neither  in  chelonia  nor  in  ophidia  is  there  any  evidence 
of  an  anterior  epiphysis,  that  is  to  say,  a  parietal  eye.  The 
first  description  of  turtles  was  given  by  Bojanus36  in  1819. 
Tiedemann395  also  mentioned  the  epiphysis  in  turtles,  but  prob- 
ably mistook  the  chorioid  plexus  for  that  structure.  Voeltz- 
kow410  in  1903,  describing  the  embryology  of  Chelone  imbricata, 
mentions  the  first  appearance  of  the  epiphysis  as  a  simple  evagi- 
nation.  Secondarily,  a  stalk  develops  between  the  pineal  organ 
and  the  roof  of  the  interbrain,  so  that,  according  to  Voeltzkow, 
the  epiphysis  in  Chelone  imbricata  separates  itself  entirely  from 
the  roof-plate.  The  pineal  region  in  chelonia  presents  the 
usual  features,  namely,  a  large  paraphysis  which  forms  an 
unusually  extensive  sac.  The  end  of  this  sac  lies  directly  over 
the  epiphysis.  The  velum  transversum  and  dorsal  sac  are 
incorporated  in  the  chorioid  plexus.  There  is  a  fairly  well 
marked  commissura  habenularis,  the  epiphysis  in  its  usual 
chelonial  form,  and  also  the  posterior  commissure.  The  form 
of  the  epiphysis  in  the  turtle  is  oval  or  ovoid;  it  lies  close  to 
the  roof-plate.  The  surface,  as  Herrick177  has  shown  in  1891, 
is  uneven  and  may  indicate  r,  process  of  lobulation.  Many 


124  FREDERICK    TILNEY   AND    LUTHER   F.    WARREN 

trabeculae  of  connective  tissue  extend  inward  toward  the  center 
of  the  organ  from  the  capsule.  The  cellular  elements  are  for 
the  most  part  ependymal  cells  and  neuroglia.  No  ganglionic 
cells  and  no  nerve  fibers  were  observed.  There  is  no  clear 
evidence  of  secretory  function  in  the  epiphysis  of  Chelonia.  The 
organ  contains  a  small  cavity. 

In  Crocodilia,  the  pineal  organ,  according  to  Sorensen  ('94)  ,363 
as  well  as  the  other  elements  of  the  epiphyseal  complex,  is  en- 
tirely absent.  In  the  roof  of  the  interbrain  there  is  a  well 
marked  commissura  habenularis  and  a  posterior  commissure 
with  possibly  a  dorsal  sac  and  a  paraphysis.  Voeltzkow410  in 
1903  found  no  epiphysis  in  Crocodilus  madagascariensis.  Rabl- 
Rtickhard316  in  1878  showed  in  Alligator  mississippiensis  a 
long,  rounded  conarium.  This  observation,  according  to  later 
observers,  is  probably  an  error,  the  paraphysis  and  chorioid 
plexus  having  been  mistaken  for  the  pineal  body. 

The  parietal  eye  in  Reptilia.  The  parapineal  element  in 
saurians  and  sphenodon  gives  rise  to  what  is  known  as  the 
third  or  parietal  eye  of  reptiles.  Among  the  saurians  it  is  not 
universally  present.  Its  absence  has  been  noted  in  certain  of 
the  Geckonidae,  as  for  example,  Hemidactylus,  Gehyra,  Gecko, 
and  Platydactylus.  It  is  also  absent  in  certain  Agamidae,  such 
as  Draco,  Ceratophora,  Lyriocephalus,  and  Moloch.  It  has  not 
been  observed  in  Tejus  and  Cyclodus.  The  general  form  of  the 
parietal  eye  is  saccular  with  the  upper  wall  corresponding  to  a 
lens  which  is  pigment  free  while  the  under  or  ventral  wall  which 
corresponds  to  the  retina  is  deeply  pigmented.  The  third  eye 
presents  several  different  forms  in  the  different  species: 

1.  It  may  be  pyriform,  as  is  the  case  in  Sphenodon,  Spencer366 
and  Ley  dig,236  and  Iguana,  Spencer.367     It  is  also  of  this  shape  in 
Varanus  nebulosus  and  Anguis,  Hanitsch,169  also  in  Pseudopus 
pallasi,  Studnicka.386 

2.  Dorsoventrally   elongated    and    ovoid    as    in  Anolis    and 
Lyriocephalus,  Spencer.367 

3.  Spherical  or  hemispherical,  in  which  latter  case  the  lens  is 
flattened,    as    in    Lacerta    ocellata,    Chameleon,   Grammatophora 
barbata,   Moloch   horridus,  and   Agama   hispida,    Ley  dig238    and 
Spencer.368 


THE    PINEAL    BODY 


125 


4.  Lenticular    and  flattened,   as  in  Anguis  frcgilis,  Lacerta 
vivipara,  Lacerta  agilis,  Lacerta  viridis,  Seps  tridactylus,  Varanus 
giganteus,  Plica,  Iguana,  and  Calotes. 

5.  Flattened    so    that   the   under   wall    is    pressed    inward, 
as    in    Varanus    bengalensis,  Leiolaemus    nitidus,    and    Calotes 
ophiomachus. 

6.  Flattened  and  decidedly  elongated,  as  in  Seps  chalcidica 
and  Calotes  versicolor. 


Fig.  64    The  pineal  eye  of  Anolis,  according  to  Spencer,  1886 

While  the  dorsal  wall  of  the  parapineal  vesicle  forms  the  true 
lens  of  the  parietal  eye,  the  ventral  wall  is  pigmented  and  gives 
rise  to  the  retina.  The  latter  consists  of  layers  of  different 
types  of  cells.  In  the  embryonic  stages  it  is  attached  to  the 
brain  by  a  tubular  prolongation  from  the  roof-plate.  The  first 
detailed  description  of  the  parietal  or  third  eye  in  reptiles  was 
given  by  deGraaf155  in  1886.  Spencer's366  work  appeared  in 
the  same  year,  and  a  number  of  investigations  have  been  reported 
since  then  confirming  in  a  general  way  the  conclusions  of  these 


126 


FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 


early  workers.  These  researches  include  those  of  Beraneck 
('87)21  in  Anguis  and  Lacerta;  Francotte  ('87)127  in  Anguis; 
McKay  ('88)255  in  Grammatophora  and  Hinulia;  Strahl  and 
Martin  (J88)383  in  Lacerta,  and  Ritter  ('91)332  in  Phrynosoma. 
There  is  a  general  agreement  regarding  the  histological  structure 
of  the  retina  among  saurians,  and  the  following  layers  have 
been  identified  by  most  of  the  investigators  mentioned  : 


Fig.  65    The  structure  of  the  retina  in  the  pineal  eye  in  Sphenodon  punctatum, 
according  to  Spencer,  1886. 

1.  An  inner  layer  of  long,  cylindrical  cells,  called  the  rods  or 
rod-like  bodies  of  Spencer366  or  the  cellules  batonnets  of  Fran- 
cotte.127   In  these  cells  pigment  occurs. 

2.  An  inner  layer  of  cells,  called  the  'couche  cellulaire  interne' 
by  Francotte.127     This  consists  of  round  cells  with  a  large  round 
nuclei.     Ritter332  distinguishes  two  types  of  nuclei  in  this  layer, 
namely,  those  which  are  round  and  small  and  those  which  are 
oval  and  long. 


THE    PINEAL   BODY 


127 


3.  A  molecular  layer  described  by  Spencer366  and  Francotte127 
or  a  layer  of  nerve  fibers  described  by  Strahl  and  Martin.383 
The  latter  observers  and  Klinckowstroem206  maintain  that  these 
fibers  are  in  connection  with  the  parietal  nerve.     Leydig238  and 
Dendy86  believed  that  a  cleft  occurred  in  this  layer  which,  ac- 
cording to  Leydig,  gives  rise  to  a  lymph  space. 

4.  An  outer  cellular  layer  of  round  cells  somewhat  deeper  than 
the  second  layer. 

5.  A  membrana  limitans  externa. 


Fig.  66  The  pineal  eye  in  Iguana  tuberculata,  according  to  Klinckowstroem, 
1894. 

The  most  important  elements  in  the  retina  are  the  rod  cells 
which  appear  to  correspond  to  the  ependymal  cells  of  the  retina 
in  the  pineal  organ  of  Petromyzon.  They  are  long,  cylindrical 
elements  in  which  may  be  differentiated  an  outer  thread-like 
part  and  a  more  cylindrical  portion.  The  nucleus  occupies  an 
enlargement  in  the  area  of  transition  between  these  two  por- 
tions. The  inner  cylindrical  parts  lie  close  together;  the  outer 
thread-like  parts  have  broad  spaces  between  them  in  which 
are  lodged  neuroglia  and  some  ganglionic  cells.  The  peripheral 
processes  come  to  the  surface  of  the  retina  and  spread  out  against 


128  FREDERICK    TILNEY   AND    LUTHER    F.    WARREN 

the  membrana  limitans  externa.  The  pigment  in  the  cells  is  in- 
some  cases  arranged  in  transverse  bands  or  stripes,  according 
to  Spencer366  in  Sphenodon  and  Ley  dig  ('9 1),238  in  Anguis.  All 
of  the  rod  cells  are  similar.  The  connection  of  the  retinal  ele- 
ments with  fibers  of  the  parietal  nerve  is  not  yet  altogether 
understood.  In  adults  the  organ  is  rudimentary.  It  is  not 
known  whether  the  nerve  fibers  come  from  the  large  retinal 
elements,  from  the  ganglionic  cells  of  the  deep  retinal  layer,  or 
from  the  large  cylindrical  cells  of  the  inner  layer.  The  latter 
seems  most  probable  in  view  of  the  conditions  in  Petromyzon. 

The  parietal  nerve.  This  nerve  was  first  described  by  Spencer366 
in  1886  and  has  been  observed  by  many  others  since  then. 
Spencer  believes  that  the  parietal  nerve  is  connected  with  the 
end  of  the  epiphysis,  that  is  to  say,  a  direct  continuation  of  the 
pineal  organ.  The  entire  course  of  the  parietal  nerve  from  the 
parietal  eye  to  the  brain  roof  was  first  traced  by  Strahl  and 
Martin383  in  1888  in  older  embryos  of  Lacerta  vivipara  and 
A nguis  fragilis.  These  observers  showed  that  the  nerve  was 
completely  independent  of  the  epiphysis.  Beraneck23  in  1892 
made  more  exact  studies  and  confirmed  the  view  of  Strahl  and 
Martin.  Other  authors  are  also  emphatic  in  stating  the  com- 
plete independence  between  the  epiphysis  and  the  parietal  eye. 
Among  them  are  Studnicka  ('93), 384  in  Lacerta;  Klinckowstroem 
('94)209  in  Iguana;  Leydig  (J96)239  and  Bendy  (799)87  in  Spheno- 
don, and  Schauinsland  ('03)347A  also  in  Sphenodon.  The  parietal 
nerve  begins  to  develop  shortly  after  the  separation  from  the 
roof  of  the  parietal  eye.  Of  the  direction  of  its  fibers,  whether 
from  the  brain  to  the  eye  or,  as  is  the  case  in  the  pineal  organ 
and  the  paired  eyes,  from  the  eye  to  the  brain,  there  is  no  proof. 
The  latter  course,  however,  is  most  probable.  In  Anguis,  the 
parietal  nerve  first  appears  at  50  mni.  embryo  size  and  reaches 
its  maximum  of  development  between  the  27  and  30  mm.  size. 
In  Iguana,  the  nerve  is  well  developed  at  fourteen  days  and  is 
at  its  maximum  at  twenty-four  to  twenty-six  days.  Between 
the  thirtieth  and  fortieth  days  it  shows  signs  of  reduction. 
Strahl  and  Martin383  showed  that  the  nerve  comes  into  relation 
with  the  ganglionic  cells  forming  a  prominence  with  the  brain 


THE    PINEAL    BODY 


129 


roof.  This  Beraneck23  designated  in  1892  as  the  noyau  parietal. 
The  prominence  thus  described  can  be  nothing  else  than  the 
closely  set  ganglia  habenulae  of  the  interbrain  as  shown  by 
Studnicka384  in  1893  in  Lacerta,  by  Klinckowstroem209  in  1894 
in  Iguana,  and  by  Leydig239  in  1896  in  Lacena.  The  parietal 
nerve  is  made  up  of  fine  fibrils;  it  has  a  perineurium,  a  connec- 


»* ; 


Fig.  67     The  pineal  eye  of  Varanus  giganteus,  according  to  Spencer,  1886. 
Pa.,  parapineal  organ;  Npar.,  parapineai  nerve;  Bl.,  blood  vessel. 

tive  tissue,  and  glial  sheaths.  In  Iguana  it  degenerates  and 
disappears  in  the  adults,  according  to  Klinckowstroem  ('94). 20<J 
In  some  cases  Spencer366  found  the  parietal  nerve  divided  into 
two  or  three  strands,  for  example,  in  Lacerta  ocellata  and 
Varanus  gigameus.  A  similar  splitting  was  found  by  Studnicka384 
in  1893  in  Petromyzon.  Klinckowstroem209  in  Iguana  recognized 
a  second  parietal  nerve  which  arose  from  the  left  habenular 


MEMOIR   NO.   9 


130  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

ganglion  and  passed  close  behind  the  first  nerve  to  the  parietal 
eye.  The  lens  of  the  parietal  eye  is  not  uniform  in  its  shape; 
it  occurs  in  the  following  different  forms: 

1.  Regular  bi-concave  lens,  both  surfaces  curved,  which  is 
most  common  in  Lacerta  vivipara,  Lacerta  agilis  and  Lacerta 
ocellata,  Leiolaemus   nitidus,  Seps   chalcidica,  Phrynosoma  doug- 
lassi,  and  Sphenodon. 

2.  Bi-convex,  with  the  under  surface  more  convexed  than  the 
upper,  as  in  Anolis  and  Sphenodon. 

3.  Plano-convex,  as  in  Anguis  and  Iguana. 

4.  Concavo-convex,  as  in  Calotes,    Varanus  bengalensis,  and 
Varanus  giganteus. 

The  structure  of  the  lens  is  made  up  of  peculiar,  long,  cylin- 
drical cells  apparently  derived  from  modified  ependymal  cells. 
These  are  the  so-called  lens  cells.  There  are  some  intercellular 
spaces,  probably  lymph  spaces,  according  to  Leydig  ('91). 238 
The  lens  cells  are  nearly  free  of  pigment.  The  substance  of  these 
cells  is  very  hard.  Their  nuclei  are  oval  or  round  and  are  sel- 
dom scattered  over  the  entire  lens  surface  or  its  entire  thick- 
ness. They  are  most  numerous  at  the  border  of  'the  lens  where 
the  latter  passes  over  into  the  retina. 

The  parietal  foramen.  Leydig234  in  1872  found  a  round  or  oval 
opening  in  the  skull  of  Sphenodon  situated  in  the  osparietal, 
which  seemed  either  directly  to  serve  as  the  outlet  for  the  parietal 
organ  or  else  for  the  entrance  of  light  rays.  It  was  reminiscent 
of  a  similar  opening  in  the  cartilaginous  roof  of  the  cranium  in 
selachians.  In  most  cases  the  parietal  eye  is  in,  or  directly 
under,  this  foramen.  Species  which  do  not  possess  a  parietal 
eye  have  a  parietal  foramen  which  is  filled  by  the  pineal  organ, 
in  which  case,  the  end-vesicle  takes  the  place  of  a  third  eye  as 
far  as  location  is  concerned.  The  foramen  is  absent  in  a  large 
number  of  saurians,  particularly  in  the  Geckonidae,  and  it  is 
also  absent  in  Ceratophora  aspera.  There  are  also  instances  in 
which  the  foramen  does  actually  appear  in  some  individuals  of  a 
species  and  yet  in  other  individuals  of  the  same  species  it  is  closed 
by  bone.  The  eye  usually  lies  in  the  middle  of  this  foramen  or 
near  its  upper  edge.  The  relation  between  eye  and  foramen  is 


THE    PINEAL   BODY  131 

different  in  different  periods  of  life.  The  foramen  is  not  the 
result  of  direct  pressure  of  the  eye,  but  occurs  for  the  purpose  of 
permitting  the  passage  of  light  rays.  As  a  rule,  the  parietal  eye 
lies  in  the  foramen  or  under  it,  so  that  its  optic  axis  corresponds 
to  that  of  the  foramen.  In  Sphenodon  a  single  exception  to 
this  rule  is  noted  by  Spencer.366  Here  the  organ  is  tipped  for- 
ward so  that  the  light  rays  cannot  reach  the  entire  retina.  The 
size  of  the  foramen  differs  and  bears  no  direct  relation  to  the 
size  of  the  parietal  eye.  The  third  eye  is  connected  to  the 
foramen  by  means  of  connective  tissue  and  is  surrounded  by 
lymph  spaces  while  blood  vessels  make  up  a  net  about  the 
edges  of  the  foramen.  No  mention  of  muscular  tissue  or  dis- 
crete muscles  has  been  made  in  connection  with  the  parietal 
eye. 

Ley  dig238  in  1891  found  in  Lacerta  muralis,  near  the  tip  of 
the  epiphysis,  four  round,  free,  calcium  bodies.  Similarly  in 
Varanus  nebulosus  many  small  pieces  of  calcium  carbonate  have 
been  observed.  These,  however,  have  nothing  to  do  with  the 
more  common  deposits  of  brain  sand  in  the  pineal  organ  of 
mammals,  as  Ley  dig238  originally  thought. 

The  interior  of  the  parietal  eye  contains  a  coagulum,  the 
vitreous  or  the  corpus  vitreum.  This  consists  of  a  syncytial 
layer  of  cells  entirely  free  of  pigment.  A  sclera  has  been  de- 
scribed as  developing  in  connection  with  the  membrana  limitans 
externa  which  passes  over  into  the  connective-tissue  sheath  of 
the  eye.  There  is  a  space  between  these  two  layers  which  was 
originally  supposed  by  Ley  dig238  to  be  a  large  lymph  space.  In 
most  cases  the  connective  tissue  forms  a  sheath  for  the  eye 
which  may  be  considered  as  a  sclera.  In  other  instances  it  is 
absent.  The  connective-tissue  capsule  of  the  parietal  eye  is 
considered  analogous  to  the  sheath  of  the  eye  in  Petromyzon. 
The  connective  tissue  above  the  eye  becomes  differentiated  as  a 
cornea  and  contains  no  pigment.  It  is  almost  fiberless  connective 
tissue.  A  parietal  spot  is  absent  in  those  saurians  in  which 
no  parietal  eye  or  no  parietal  foramen  develops.  It  is  recognized 
as  a  less  pigmented  area  in  the  skin  and  presents  many  different 
appearances,  as  well  as  differences  in  size,  in  the  several  species 
of  saurians  (fig.  68). 


132 


FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 


Accessory  pineal  and  parapineal  organs  in  Reptilia.  A  number 
of  observers  have  reported  the  appearance  of  accessory  struc- 
tures in  connection  with  both  the  pineal  and  parapineal  organs. 
Such  observations  have  been  made  by  Spencer  ('86) 366  in  Plica 
umbra;  by  Duval  and  Kalt  ('89)"  in  Anguisfragilis;  by  Carriere57 
in  1890;  by  Prenant311  in  1893-94-96;  by  Leydig237  in  1890-91, 
and  by  Francotte130  in  1896.  Accessory  organs  were  also  found 


Fig.  68    The  corneal  scale  in  Calotes,  according  to  Spencer,  1886 

in  Laceria  vivipara  by  Burckhardt46  in  1894;  by  Francotte130  in 
1896;  by  Klinckowstroem  ('94) 209  in  Iguana,  and  by  Studnicka 
('93)384  in  Pseudopus  pallasi.  Accessory  epiphyseal  organs  may 
arise  either  from  the  lateral  wall  of  the  end- vesicle  of  the  pineal 
organ  or  the  under  wall  of  the  parietal  eye.  There  are  two 
types  of  accessory  organs:  1)  accessory  pineal  organs,  and  2) 
accessory  parietal  eye  organs.  The  following  are  the  possibili- 
ties for  accessory  pineal  organs : 


THE    PINEAL   BODY  133 

1.  Evaginations  of  the  distal  end  of  the  epiphysis  as  in  Anguis 
and  Iguana. 

2.  Independent   buds   off  the  epiphysis  or  extrusions  from 
it  held  in  relation  by  pigment  strands  of  cells,  as  in  Lacerta 
vivipara. 

3.  Isolated  extrusions  from  the  end  of  the  epiphysis. 
Accessory  parietal  eye  organs  are  less  common.     Carriere57 

in  1890  showed  a  diverticulum  from  the  under  wall  of  the  parietal 
eye.  Prenant312  in  1895  made  the  same  observation.  Fran- 
cotte127  found  that  these  accessories  consist  of  a  lens  and  retina 
which  are  still  in  connection  with  the  chief  organ.  Accessory 
organs  usually  have  pigment  in  them,  but  this  is  not  so  in  Phry- 
nosoma  and  Sphenodon.  Only  the  under  wall  is  pigmented  as 
a  rule,  so  that  the  under  wall  corresponds  to  the  retina  while 
the  upper  wall  corresponds  to  the  lens.  Such  accessory  organs 
attached  to  the  parietal  eye  indicate  an  attempt  to  produce 
another  optic  organ.  Only  exceptionally  does  the  upper  or 
dorsal  wall  show  a  lens  formation.  In  Pseudopus,  Studnicka384 
in  1893  found  that  the  interior  of  the  accessory  parietal  eye  con- 
tained a  syncytium  as  does  the  actual  parietal  eye.  Prenant312 
in  1895  differentiated  the  following  types  of  accessory  organs  in 
Anguis: 

1.  Epiphyseal  eye.     This  lies  close  to  the  epiphysis,  yet  sepa- 
rated from  it  and  is  entirely  derived  from  that  organ. 

2.  Interparietal-epiphyseal  eye.     This  is  situated  in  the  mid- 
line  between  the  epiphysis  and  the  parietal  eye.     It  is  the  most 
frequent  of  the  accessory  parietal  eye  organs. 

3.  Intraparietal  eye.     This  is  connected  with  the  retina  and 
under  wall  of  the  parietal  eye  or  else  is  included  in  it. 

4.  Accessory  chorioidal  eye.     This  is  found  very  infrequently. 
It  is  widely  separated  from  both  parietal  organs  and  presents 
itself  as  a  pigmented  hollow  vesicle  lying  on  the  upper  surface 
of  the  chorioid  plexus. 

Accessory  parietal  organ  structures  are  most  frequent  in 
embryos  and  tend  to  disappear  in  the  adult.  This  observation 
is  agreed  to  by  most  authors. 


134  FREDERICK    TILNEY   AND    LUTHER    F.    WARREN 

Differences  observed  in  the  epiphyseal  complex  in  the  various 

species  of  reptiles  already  investigated. 
PROSAURIANS 

1.  Sphenodon  punctatum  (Hatteria).     Spencer  ('86)  ;367  Leydig 
('91)  ;238  Hoffmann  ('90)  ;187  Dendy  ('99) 87  described  a  develop- 
ment, as  did  also  Schauinsland346  in  1899  and  1903. 

The  pineal  organ  in  the  embryo  is  a  simple  evagination  with  a 
thin  stalk  which  is  solid.  The  walls  of  the  end-vesicle  have 
many  folds.  Only  the  cells  in  the  interior  retain  a  brown  pig- 
ment. The  parietal  nerve,  according  to  Spencer,  is  a  prolonga- 
tion from  the  end  of  the  epiphysis.  Such  a  connection  does 
exist  in  some  adults,  but  is  of  a  connective  tissue  character. 
Dendy  and  Schauinsland  identified  the  actual  parietal  nerve. 
It  arises  in  front  of  the  epiphysis  and  is  independent  of  it.  The 
parietal  eye  is  conical  or  pyriform  in  shape  and  the  retina  and 
lens  are  both  well  developed.  In  older  embryos  the  nerve 
does  not  enter  the  middle,  but  rather  comes  into  relation  with 
the  posterior  third  of  the  eye.  The  structure  of  the  retina 
was  most  minutely  described  by  Spencer,  Leydig,  and  Dendy. 
It  has  rod  cells  and  several  other  layers  of  cells.  It  contains 
pigment  as  well  as  a  molecular  layer  and  a  layer  of  large  gan- 
glionic  cells.  The  lens  is  bi-convex.  The  entire  organ  is  sur- 
rounded by  a  connective  tissue  capsule.  Dendy  mentions  a 
thin-walled  sac  in  the  embryo  between  the  epiphysis  and  para- 
physis.  This  undoubtedly  is  an  accessory  organ.  Sphenodon 
has  a  parietal  foramen  and  a  superficial  apparatus  usually  con- 
nected with  the  parietal  eye. 

SATJRIANS — LACERTILIA  VERA. 

GECKONIDAE.  1.  Gecko  ver us.  Spencer  ('86). 367  In  this  spe- 
cies only  the  epiphysis  is  present.  There  is  no  parietal  foramen 
and  no  parietal  spot. 

2.  Platydactylus  muralis.     Spencer    ('86)  ;367    Leydig    ('91)  ;238 
Melchers  ('99). 269     In  this  form  there  is  no  parietal  eye,  the 
epiphysis  being  the  only  element  to  appear.     This  latter  con- 
sists of  an  end-vesicle  which  is  large  and  thick-walled  having 
no  folds;  its  stalk  is  short  and  solid.     The  entire  pineal  organ  is 


THE    PINEAL   BODY  135 

flask-shaped.     There  are  many  intercellular  spaces  in  the  end- 
vesicle.     These  same  observations  hold  good  for  Mauritanicus. 

3.  Hemidaclylus  verruculatus.     Leydig    ('91). 238    This  species 
possesses  no  parietal  eye.     There  is  an  end-vesicle  which  con- 
tains a  brown  pigment.     The  vesicle  is  drawn  out  into  a  small 
point. 

4.  Hemidactylus  mabouia.     Stemmler   ('00). 374    In  this  form 
the  pineal  organ  only  is  present  and  the  end- vesicle  is  an  atten- 
uated bud.     The  proximal  portion  of  the  stalk  is  solid.     There 
is  no  pigment  and  no  fibers  in  connection  with  the  organ. 

5.  Gehyra  oceanica.     Stemmler   ('00). 374     The  parietal  eye  is 
not  well  developed.     The  pineal  organ  alone  makes  its  appear- 
ance and  has  a  definite  end-vesicle.     The  stalk  has  a  lumen  in 
its  proximal  portion.     The  cells  in  the  end-vesicle  are  ependymal 
in  type.     There  are  no  folds  in  the  wall. 

AGAMIDAE.  1.  Draco  volans.  Spencer  ('86)  ;367  Studnicka 
('93). 384  There  is  no  parietal  eye  in  this  species.  The  pineal 
organ  is  a  broad,  dorsoventrally  compressed  end-vesicle  con- 
taining no  pigment. 

2.  Ceratophora  aspera.     Spencer  ('86). 367     In  this  form  there 
is  no  parietal  eye.     An  end-vesicle  develops,  but  there  is  no 
parietal  foramen. 

3.  Lyriocephalus    scuiatus.     Spencer     ('86). 367    There    is    no 
parietal   eye   in   this   species.     An   end-vesicle  exists  with   an 
attenuated  stalk.     There  is  no  pigment,  but  the  animal  has  a 
definite  parietal  spot. 

4.  Calotes  ophiomachus  and  versicolor.  Spencer  ('86). 367    The 
epiphysis   ends    at    the    edge   of   the   parietal   foramen.     The 
parietal  eye  is  present.     Spencer  saw  only  rods  in  the  retina. 
The  lens  is  concavo-convex.     Some  of  the  lens  cells  and  retinal 
cells  are  pigmented.     A  well-marked  parietal  foramen  is  present 
and  there  is  a  small  modified  cornea  with  parietal  spots. 

5.  Agdma    hispida.     Spencer    ('86). 367    This    species    has    a 
parietal  eye,  a  retina,  lens,  and  a  parietal  foramen,  together 
with  a  cornea  and  parietal  spot. 

6.  Grammatophora  barbata.     Spencer    ('86). 367     In  this   form 
there  was  found  some  evidence  of  a  parietal  eye,  the  under 


136  FREDERICK    TILNEY   AND    LUTHER   F.    WARREN 

wall  of  which  was  definitely  pigmented.  McKay  ('88) 255  found 
a  bi-convexed  lens,  a  go'od  retina  with  rod  cells  and  round  cells, 
a  molecular  layer,  and  also  a  spindle-celled  layer  and  peculiar, 
triangular  elements.  The  lumen  was  traversed  by  a  fine  strand. 

7.  Moloch   horridus.     Spencer    ('86). 367     In   this   species   the 
organ  is  strongly  pigmented,  more  likely  an  end-vesicle  with  a 
stalk  than  a  parietal  eye.     The  parietal  foramen  in  which  the 
organ  rests  is  present.     Both    cornea    and    parietal    spot    are 
present. 

8.  Agama   caucasica.     Owsiannikow  ('88). 295     In  this  species 
there  is  a  relatively  large  parietal  eye  with  rods  in  the  retina, 
which  latter  is  otherwise  well  developed,     There  is  also  a  lens, 
a  parietal  foramen,  a  vitreous,  cornea,  and  a  parietal  spot.     In 
one  case,   Ritter   ('94) 333  found  an  accessory  organ  which  he 
called  the  parapineal  organ.     It  was  situated  in  the  parietal 
foramen  somewhat  to  the  left  of  the  parietal  eye.     No  corium 
was  above  it.     A  common,  connective  tissue  capsule  contained 
both  organs.     The  accessory  organ  was  larger  than  the  parietal 
eye.     There  was  no  lens  or  retina  in  the  accessory  organ. 

9.  Phrynocephalus    Vlangalii.     Owsiannikow  ('88). 295    In  the 
20  mm.  embryo  this  species  has  a  parietal  eye.     The  organ  is 
deeply  pigmented. 

IGUANIDAE.  1.  Phrynosoma  orbiculare.  Studnicka  ('93). 384 
In  this  species  the  epiphysis  is  broad  and  globular  and  con- 
nected by  a  stalk  to  the  roof  of  the  brain.  It  presents  an  end- 
bud  on  its  distal  extremity.  Ependymal  cells  in  the  body  con- 
tain a  brown  pigment.  In  the  lumen  there  is  a  coagulum  which 
consists  of  a  syncytium  of  pigment-containing  cells.  The  pari- 
etal nerve  was  not  observed.  The  parietal  eye  is  small,  dorso- 
ventrally  flattened  with  a  well-developed  lens  and  retina.  The 
lens  is  bi-convex.  The  cells  of  the  lens  have  their  nuclei  situated 
near  the  under  surface.  The  retina  is  filled  with  pigment,  hid- 
ing its  main  structure.  The  position  of  the  parietal  eye  is  in  a 
wide  foramen,  four  times  as  large  as  the  parietal  eye  itself.  The 
parietal  cornea  and  spot  are  present. 

2.  Anolis.  Spencer  ('86). 367  This  species  presents  a  well-devel- 
oped parietal  eye  which  is  ovoid  in  form  and  has  a  well-developed, 


THE    PINEAL   BODY  137 

thick  retina.  The  latter  is  pigmented  and  contains  rod  cells. 
The  lens  is  bi-convex.  What  Spencer  considered  a  nerve  was  in 
all  probability  connective-tissue  remains  of  a  former  nerve.  A 
narrow  parietal  foramen  occurs  while  the  cornea  and  parietal 
spot  are  absent. 

3.  Leiolcemus    niiidus.     Spencer    ('86). 367    In  this  form   the 
epiphysis  exists  as  a  hollow,  proximal  part  and  a  horizontal 
solid  end  portion.     The  latter  is  stretched  forward  to  reac    the 
parietal  foramen.     The  parietal  eye  is  dorsoventrally  flattened 
and  has  a  narrow  lumen.     The  upper  surface  of  the  retina  is 
flat  and  horizontal.     The  lens  is  present.     There  are  rod  cells 
which  are  the  chief  elements  in  the  retina.     The  lens  is  bi- 
convex and  the  nuclei  of  the  lens  cells  lie  in  a  layer  deeply 
situated.     There  is  a  parietal  foramen  in  which  the  eye  is  lodged. 
The  corium  is  clear.     There  is  a  light  colored  parietal  spot. 

4.  Leiolaemus    tennis.     Spencer   ('86). 367    The   epiphysis  ex- 
tends forward  to  a  well-marked  parietal  eye.     There  is  no  con- 
nection between  the  two.     The  parietal  eye  has  a  pigmented 
retina  and  a  lens.     The  parietal  cornea  and  parietal  spot  are 
present. 

5.  Plica  umbra.     Spencer  ('86). 367    The  epiphysis  has , a  prox- 
imal part  and  a  horizontal  portion  which  is  solid  and  reaches  the 
parietal  eye.     The  latter  is  connected  with  the  epiphyseal  end- 
sac.     The  parietal  eye  is  much  flattened  and  the  retina  is  pig- 
mented.    It  is  situated  in  a  deep  parietal  foramen.     The  cornea 
is  present  as  well  as  the  parietal  spot. 

6.  Iguana    tuberculata.      Spencer    ('86)  ;367     Leydig     ('96)  ;239 
Klinckowstroem   ('93). 207    In  this  form  the  epiphysis  is  well 
developed  with  a  large  end-bud  in  connection  with  the  proximal 
portion.     The  latter  has  a  more  or  less  follicular  appearance. 
In  embryos  the  cells  have  cilia,  but  these  later  disappear.     Klinc- 
kowstroem in  the  18  mm.  embryo  describes  a  tractus  pinealis  in 
the  distal  end  of  the  epiphysis.     A  parietal  nerve  is  described  by 
the  same  author  in  1894.     In  embryonic  stages  it  connects  the 
retina  with  the  roof  of  the  brain.     The  parietal  eye  is  globular 
and  in  some  forms  a  highly  differentiated  retina  is  present.     An 
actual  nerve  layer  appears  only  in  the  embryo  and  later  disap- 


138  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

pears.  The  pigment  increases  in  the  older  animals.  The  lens 
is  plano-concave.  The  eye  rests  in  a  parietal  foramen.  The 
cornea  is  present  as  well  as  a  marked  parietal  spot. 

7.  Phrynosoma  douglassi.     Ritter   ('91). 332     There  is  an  epi- 
physeal  vesicle  in  this  form  and  a  posteriorly  flattened  vesicle 
which  contains  no  lumen.     It  is  connected  by  a  very  thin  stalk 
to  the  epiphysis.     The  parietal  eye  is  connected  with  the  brain 
roof  and  is  a  laterally  compressed  vesicle.     The  lens  and  retina 
are  both  well  developed.     The  retina  has  an  outer  cell  layer,  a 
molecular  layer,  and  an  inner  layer  with  two  elements,  one  round 
and  the  other  elongated,  and  finally  an  inner  layer  of  rod  cells. 
There  is  a  coagulum  in  the  cavity  of  the  eye  vesicle.     The  lens 
is  slightly  bi-convex.     The  nuclei  of  the  lens  cells  lie  near  the 
inner  periphery  of  the  lens.     The  position  of  the  eye  is  in  a 
broad  foramen.     The  parietal  cornea  and  pit,  as  well  as  a  pari- 
ietal  spot,  are  all  present. 

8.  Uta  stansburiana.     Ritter  ('91)  ;332  Studnicka  ('95).386     The 
parietal  eye  in  this  form  is  also  ventrally  flattened.     The  lens  is 
separated  from  the  retina.     There  is  deep  pigment  in  the  retina 
and  the  eye  rests  in  a  parietal  foramen. 

9.  Sceleporus  undulatus.     Herrick   ('9 1)178   in  describing   the 
epiphysis  in  this  form,   states  that  the  .under  wall  has  some 
similarity  to  the  retina. 

10.  Phrynosoma  coronatum.     Ritter  ('91)  ;332  Sorensen  ('93).361 
The  epiphysis  is  similar  to  that  in  Phrynosoma  douglassi.     It  is  a 
thick-walled  vesicle.     The  cells  in  the  interior  are  deeply  pig- 
mented.     There  is  a  connective-tissue  strand  running  to  the 
parietal  eye.     The  parietal  nerve  extends  from  the  commissura 
posterior  to  the  parietal  eye.     The  eye  is  not  as  well  differ- 
entiated as  in  Phrynosoma  douglassi,  although  it  is  present. 

11.  Sceleporus  striatus.     Sorensen  ('94). 363      In  this  form  the 
epiphysis  is  attached  to  the  roof  by  a  thin,  peculiarly  white 
stalk.     The  parietal  nerve  presents  no  peculiarities,  but  arises 
from  the  anterior  portion  of  the  commissura  habenularis.     It  is 
solid  to  the  extreme  end  of  the  epiphysis  where  it  proceeds  to 
the  parietal  eye,  the  latter  apparently  being  independent  of  the 
end  of  the  epiphysis.     No  parietal  foramen  is  present.     The 


THE    PINEAL   BODY  139 

parietal  eye  has  the  form  of  a  dorsoventrally  compressed  sac 
which  has  a  lens  and  well-marked  retina,  the  latter  has  a  double 
layer  of  well-pigment ed  cells.  Rod  cells  also  are  present.  The 
entire  parietal  organ  is  enclosed  in  a  connective-tissue  capsule. 

ANGUIDAE.  1.  Anguis  fragilis.  Leydig  ('96)  ;239  deGraaf 
('86)  ;155  Spencer  (86)  ;368  Beraneck  ('92)  ;23  Hanitsch  ('88);169A 
Strahl  and  Martin  ('88)  ;383  Francotte  ('96)  ;130  Owsiannikow 
('88)  ;295  Duval  and  Kalt  ('89;)99  Carriere  ('90)  ;57  Prenant, 
('95) ,312  and  Studnicka  ('93). 384 

The  epiphysis  in  this  species  consists  of  a  proximal  and  a 
distal  portion.  The  end  portion  of  the  epiphysis  is  deeply 
pigmented.  The  parietal  eye  is  connected  by  a  connective- 
tissue  strand  to  the  epiphysis.  The  parietal  nerve  is  present 
only  in  embryos  and  arises  from  the  ganglion  habenulae.  The 
parietal  eye  is  lenticular  in  form,  dorsoventrally  flattened,  and 
has  a  deeply  pigmented  retina.  The  lens  is  bi-convex  and  plano- 
convex. The  lumen  contains  a  coagulated  substance  with  a 
syncytium.  There  is  a  well-developed  capsule.  Accessory 
organs  are  common.  The  position  of  the  eye  is  in  a  parietal 
foramen.  The  parietal  cornea,  pit,  and  spot  are  present. 

2.  Varanus  bengalensis.     Spencer  ('86). 368    The  pine'al  organ 
has  a  distal  and  proximal  portion  and  there  is  no  parietal  nerve. 
The  parietal  eye  is  present  and  contains  a  lumen.     The  retina 
contains  rod  cells  and  several  layers  of  smaller  cells.     The  lens 
is    convexo-concave.     The   parietal   foramen   is    of   large   size. 
There  is  a  capsule,  a  parietal  pit,  and  a  parietal  spot. 

3.  Varanus  nebulosus.     Leydig    ('91). 238     In   this  species  the 
pineal  organ  is  as  in  other  forms,  but  there  is  no  end-sac.     The 
parietal  eye  is  pyriform  but  there  is  no  distinct  retina. 

4.  Pseudopus     pallasi.      Owsiannikow     ('88)  ;295     Hoffmann 
('90), 187  in  Bronns  "Klassen  and  Ordnungen." 

In  this  form  there  is  a  well-developed  lens,  retina,  and  vitreous. 
Studnicka386  in  1895  described  the  conditions  as  follows:  There 
is  a  complete  pineal  organ  with  an  end-vesicle,  a  stalk,  and 
proximal  portion,  the  latter  being  the  epiphysis.  This  is  con- 
nected with  the  brain-roof  by  a  secondary  stalk.  The  parietal 
eye  is  semiglobuiar  in  shape.  There  is  a  lens  and  retina,  the 


140  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

latter  having  rod  cells,  a  layer  of  small  cells  and  a  layer  of  large, 
probably  ganglionic,  cells.  There  is  a  parietal  nerve  and  a  con- 
nective-tissue strand  connecting  the  organ  to  the  epiphysis. 
The  lens  is  bi-convex.  An  accessory  organ  is  also  present. 
There  is  a  capsule  of  connective-tissue  and  a  broad  parietal 
foramen.  A  parietal  cornea,  pit,  and  spot  also  exist. 

5.  Varanus  giganteus.     Spencer  ('86). 368     In  this  form  there  is 
no  mention  of  an  epiphysis.     The  parietal  nerve  has  a  special 
feature.     From  the  end  of  the  epiphysis  to  the  parietal  eye  such 
a  nerve  is  seen  to  extend.     Two  or  three  strands  of  the  nerve 
are  found  which  become  confluent.     The  parietal  eye  is  dorso- 
ventrally  flattened.     There  is  a  lens  and  retina  present,   the 
latter  contains  rod  cells  and  several  other  layers.     In  the  cavity 
there  is  a  vitreus.     The  lens  is  thin  and  bi-convex.     In  the 
center  is  a  mass  of  round  cells  deeply  pigmented  indicative  of  a 
rudimentary  character  of  the  organ.     The  parietal  capsule  con- 
sists of  connective  tissue.     There  is  a  parietal  foramen,  pit,  and 
spot. 

6.  Varanus  griseus.     Edinger  (00). 106    This  species  shows,  in 
a  sagittal  section   through  the  brain,  an  unusually  large  epi- 
physis thrown  into  many  folds.     It  resembles  the  epiphysis  of 
Pseudopus. 

TEJIDAE.  1.  Ameiva  corvina.  Spencer  ('86). 366  In  this  form 
neither  a  parietal  foramen  nor  a  corneal  pit  is  present. 

2.  Tejus  teguixin.  Klinckowstroem  ('94).209  An  embryo  of 
this  form  seemed  to  show  only  a  pineal  organ  well  developed, 
while  above  it  was  a  rudimentary  parietal  eye.  Studnicka384 
does  not  believe  the  parietal  eye  develops  in  this  form. 

LACERTIDAE.  1.  Lacerta  vivipara.  Spencer  ('86)  ;366  Owsian- 
nikow  ('88)  ;295  Strahl  and  Martin  ('88)  ;383  Leydig  ('91)  ;238  Stud- 
nicka ('93). 384  In  this  species  the  pineal  organ  is  globular  and 
pyriform;  its  extremity  alone  contains  pigment.  This  is  con- 
nected with  the  parietal  eye  by  a  vascular  connective-tissue 
strand.  The  parietal  nerve  is  independent  of  this  strand. 
The  parietal  eye  is  a  flattened  vesicle  and  there  is  a  much-re- 
duced lumen.  The  retina  is  deeply  pigmented;  its  structure  is 
obscured  by  this  vesicle.  The  lens  is  bi-convex.  The  capsule 


THE    PINEAL   BODY  141 

is  not  well  developed.     The  eye  eventually  makes  its  way  into 
the  parietal  foramen.     The  corneal  pit  is  present. 

2.  Lacerta  viridis.     Spencer  (r86);366  Leydig  ('91). 238    In  this 
form,  extending  from  the  parietal  organ  into  the  epiphysis  is 
a  fibrous  strand.     The  end  of  the  epiphysis  is  deeply  pigmented. 
The  parietal  eye  is  flattened  dorsoventrally.     The  retinolen- 
ticular  transition  is  gradual.     There  is  much  pigment  in  the 
retina.     The  lens  is  bi-convex.     The  parietal  foramen  is  present. 
There  is  a  corneal  pit,  cornea,  and  a  parietal  spot. 

3.  Lacerta    ocellata.     Spencer    ('86) ;366  Leydig    ('91).238     The 
pineal  organ  is  expended  at  its  distal  end  with  an  end-sac  proc- 
ess.    The  wall  is  folded  to  form  twelve  accessory  spaces  in  the 
epiphysis.     The  end  of  the  epiphysis  is  pigmented.     There  is  a 
parietal  nerve  and  a  well-developed  parietal  eye  which  is  globu- 
lar and  slightly  flattened.     The  retinolenticular  transition  is 
gradual.     The  retina  is  pigmented  and  contains  cylindrical  and 
ganglionic  cells.     The  lens  is  bi-convex.     The  capsule  is  well 
developed.     The    parietal    foramen    contains    the    eye.     The 
parietal  cornea  is  present.     There  is  also  the  parietal  spot. 

4.  Lacerta    agilis.     Owsiannikow     ('88)  ;295     Leydig     ('91)  ;238 
Studnicka  ('93). 384    The  pineal  organ  is  present  in  the  form  of  an 
epiphysis,  which  is  saccular  and  has  a  hollow  stalk.     The  parietal 
nerve,  according  to  Leydig  ('96), 239  is  present.     It  takes  origin  in 
the  ganglion  habenulae  and  extends  to  the  parietal  eye.     This 
eye  is  a  flattened,  saccular  vesicle.     The  retina  and  lens  are 
sharply  demarcated.     The  retina  is  less  pigmented  than  in  other 
forms.     It  is  connected  with  the  brain  by  a  parietal  nerve.     The 
lens  is  bi-convex.     There  is  a  special  parietal  sheath  made  up  of 
connective   tissue.     The    parietal    foramen,     corneal    pit,    and 
parietal  spot  are  present.     Exceptionally,  the  foramen  is  closed 
by  bone. 

5.  Lacerta    muralis.     Leydig     ('91)  ;238      Studnicka     ('93)  ,384 
The  epiphysis  is  present  as  is  also  the  parietal  eye.     The  retina 
is  deeply  pigmented.     The  corneal  pit  and  parietal  spot  are 
also  present. 

SCINCIDAE.     1.  Cyclodus  gigas.     Spencer  '86). 366    The  pineal 
organ  arches  forward  over  the  hemispheres  to  enter  the  region 


142  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

of  the  parietal  foramen.  The  epiphysis  is  hollow.  The  stalk 
opens  into  the  ventricle.  The  proximal  tubular  portion  is 
present.  The  distal  portion  is  within  the  foramen.  The  end- 
vesicle  of  the  pineal  organ  comes  into  this  relation.  Spencer 
thought  it  was  a  rudimentary  eye.  The  corneal  pit,  parietal 
foramen,  and  parietal  spot  are  present. 

2.  Chalcides    tridactylus.     Spencer    ('86)  ;366    Leydig    ('91). 238 
The  epiphysis  is  a  globular  vesicle.     The  end  is  prolonged  into  a 
tapering   process.     The   epithelium   is   much    thickened.     The 
parietal  eye  is  separate  from  the  epiphysis.     The  retinolenticular 
transition  is  gradual.     The  lens  is  bi-convex.     There  is  a  parietal 
foramen,  cornea,  spot,  and  pit. 

3.  Hinulia.     McKay  ('88) ;255  Sorensen  ('94). 363     In  this  form 
there  is  a  well-developed  parietal  eye  which  is  unattached  to 
the   epiphysis.     The   lens   is   bi-convex.     The   retina   contains 
rod  cells,  round  cells,  a  molecular  layer,  spindle  cells,  and  pig- 
ment cells. 

4.  Scincus  officianalis.     Prenant  ('96). 313     There  is  a  parietal 
eye  and  a  parietal  foramen  well  developed  in  this  form. 

5.  Gongylus    ocellatus.     Legge    ('96). 228     In    an    embryonic 
study  of  this  form  the  epiphysis  with  a  proximal  portion  and  a 
distal  part  was  present.     Only  in  the  embryonic  stages  was  the 
parietal  eye  observed.     It  contains  a  brown  pigment.     There  is 
a  lens  which  is  bi-convex.     The  parietal  nerve  is  not  present. 
The  parietal  cornea,  foramen,  and  spot  were  not  observed. 

CHAMAELEONTIDAE.  1.  Chamaeleon  vulgaris.  Spencer  ('86)  ;366 
Owsiannikow  ('88);2y5  Studnicka  ('93). 384  The  pineal  organ  in 
the  form  of  the  epiphysis  is  a  folliculated,  hollow  sac,  which  is 
flexed  forward,  the  walls  being  much  flattened.  It  runs  out  into 
a  long,  strand-like  point.  The  parietal  nerve  is  probably  not 
present  in  the  adult.  The  connection  between  the  pineal  organ 
and  the  eye  is  connective  tissue  and  not  nerve.  As  to  the  pari- 
etal eye,  authors  differ;  some  say  there  is  a  good  lens  and  retina, 
others  regard  this  as  rudimentary  in  all  respects.  There  is  a 
good  capsule  and  a  good  parietal  foramen.  The  parietal  cornea, 
pit,  and  spot  are  absent. 

OFHIDIA.  1.  Python  ligris.  Rabl-Ruckhard  ('94). 323  In 
this  species  there  is  an  oval-shaped  glandular  structure,  having 


THE    PINEAL   BODY  143 

many  reduplications  in  its   walls.     It   is  rich  in  blood  vessels 
and  has  a  small  cell  content.     Over  it  lies  the  chorioid  plexus. 

2.  Eutaenia  sirtalis.     Sorensen  ('94). 363     The  epiphysis  in  this 
species  is  globular  in  form  and  glandular  in  structure.     It  is 
embedded  in  connective  tissue.     Herrick  ('91) 176  agrees  in  these 
observations. 

3.  Tropidonotus  natrix.     Studnicka    ('93) ;384  Leydig    ('97).24° 
In  this  form  there  is  a  paraphysis  and  epiphysis  in  older  embryos 
and  in  the  adult.     The  epiphysis  is  definitely  glandular  in  char- 
acter.    There  is  a  thin  stalk,    the  latter   probably   secondary 
and  not  analogous  to  the  stalk  in  lower  forms.     Ssobolew364  in 
1907,  working  on  embryos  of  Tropidonotus  natrix  and   Viper  a 
berus,  found  that  the  epiphysis  develops  earlier  than  the  para- 
physis.    The  parietal  eye  does  not  appear  in  either  of  the  forms 
studied,  nor  is  there  a  parietal  foramen.     The  cells  of  the  epi- 
physis are  arranged  in  colonies  as  in  the  glands  of  internal  secre- 
tion.    The  organ  seems  to  have  nothing  to  do  with  light  per- 
ception and  the  same  applies  to  heat  perception.     There  is  no 
parietal  nerve  and  the  primitive  canal  in  the  organ  is  lost  (fig.  69). 

4.  Tropidonotus     rhombifer.      Sorensen     ('94)  ,363     The     epi- 
physis is  glandular  in  character. 

5.  Bascanium  constrictor.     Sorensen  ('94). 363     In  the  embryo 
of  this  species  the  epiphysis  has  a  glandular  form  and  is  con- 
nected with  a  stalk  to  the  roof  of  the  interbrain  (fig.  70). 

6.  Coluber    aesculapii.     Studnicka    ('93). 384     In   this    species 
the  epiphysis  is  globular  in  form  and  covered  with  connective 
tissue.     It  contains  a  dark  pigment  and  lies  close  to  the  brain. 

7.  Coronella  austriaca.     Leydig  ('97).24°     There  is  no  parietal 
organ  in  this  species  in  relation  with  the  skull.     In  the  embryo 
the  epiphysis  is  well  developed. 

8.  Pelias    berus.     Hanitsch    ('88);169A  Studnicka  ('93). 384     In 
this  species  Hanitsch  believed  that  he  discerned  a  parietal  organ 
with  much  pigment  and  a  lens.     Studnicka  disagrees  with  this 
and  describes  the  epiphysis  as  a  typically  glandular  structure. 

9.  Vipera  ursinii.     Leydig  ('97).24°     In  this  species  the  struc- 
ture is  definitely  glandular. 

CHELONIA.     1.  Chelone  my  das.     Rabl-Ruckhard  ('86). 322    In 
this  species  the  epiphysis  is  a  massive,  bilobed  structure. 


144 


FREDERICK    TILNEY    AND   LUTHER   F.    WARREN 


2.  Cistudo  europaea.  Bojanus  ('19).36  This  author  first 
described  the  epiphysis  in  this  form  as  a  short,  pediculated  struc- 
ure  with  a  dilated  extremity  which  was  flexed  forward.  Faivre115 
in  1857  describes  it  as  a  conical  body  containing  small  particles  of 
calcium  phosphate.  Herrick176  in  1891  defined  it  as  a  lobulated 
sac  attached  to  the  roof  of  the  brain.  The  distal  portion  is  non- 
vascular.  Sorensen  ('93), 361  reconstructed  the  pineal  organ  in 
this  form  (fig.  71). 


Fig.  69    The  epiphyseal  complex  in  a  young  Tropidonotus  natrix,  according 
to  Leydig,  1897. 

3.  Aspidonectes    spinifer.     Herrick    ('9 1).176     In    this   species 
the  epiphysis  has  the  form  of  a  tubular  structure  arching  for- 
ward.    Its  lumen  opens  into  the  ventricle  through  a  short  stalk. 

4.  Chelydra    serpentina.     Humphrey    ('94).19°     The    embryo 
of  this  species  has  the  same  form  as  the  saurians.     In  the  early 
stages  it  is  a  dilated  sac  connected  with  the  third  ventricle  by  a 
short  stalk.     Later  this  stalk  becomes  hollow  and  in  adults  it 
shows  lobulation. 


THE    PINEAL   BODY 


145 


5.  Amida    mutica.     Gage     ('95). 136    The    epiphysis    in    this 
species  is  similar  to  other  chelonians. 

6.  Chelone  imbricata.     Voeltzkow  ('03).41°     The  epiphysis  in 
this  species  is  entirely  separated  from  the  brain. 


Fig.  70  The  pineal  region  of  Boscanium  constrictor,  according  to  Sorensen, 
1894. 

P/.,  paraphysis;  Ds.,  dorsal  sac;  Ch.,  commissura  habenularis;  Ep.,  proxi- 
mal portion  of  pineal  organ;  Sch.,  pars  intercalaris  posterior;  cp.,  posterior 
commissure. 

Crocodilia.  Sorensen  ('94). 363  As  already  stated,  this  author 
did  not  find  the  epiphysis  or  any  portion  of  the  parietal  organ 
in  the  alligator.  Voeltzkow410  in  1903  in  Crocodilus  madagas* 
cariensis  found  no  epiphysis  (fig.  72). 

The  conditions  and  relations  of  the  epiphyseal  complex 
in  Reptilia  are  so  important  as  to  necessitate  the  following 
tabulation : 

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THE    PINEAL   BODY 


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Fig.  71     The  pineal  body  of  Cistudo  europaea.  according  to  Sorensen,  1896. 
Fig.  72     The  pineal  region  in  the  Alligator,  according  to  Sorensen,  1896. 
P/.;  paraphysis;  Ds.,  dorsal  sac;  Ch.,  commissura  habenularis;  Cp.,  posterior 
commissure;  M.,  midbrain. 


148  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

The  parietal  or  third  eye  does  not  make  its  appearance  in 
reptiles  except  in  Sphenodon  and  Lacertilia  vera.  In  these 
latter  forms  it  is  by  no  means  constant.  Of  forty-four  species 
examined,  the  parietal  eye  has  been  observed  in  29  instances, 
the  retina  in  28,  the  lens  in  24,  the  parietal  nerve  in  25,  the 
cornea  in  24,  and  the  parietal  foramen  in  28.  It  was  impossible 
to  detect  these  structures  in  the  same  number  of  species  as 
follows:  Parietal  eye  absent  in  9,  retina  absent  in  11,  lens  absent 
in  10,  nerve  absent  in  12,  cornea  absent  in  10,  and  parietal  fora- 
men absent  in  10.  The  pineal  organ,  either  complete  in  all  its 
three  portions  or  as  the  proximal  portion  (epiphysis  proper), 
was  present  in  all  of  the  forty-four  species.  A  complete  pineal 
organ  was  observed  in  thirty-one  species  while  a  highly  devel- 
oped proximal  portion,  possibly  suggestive  of  glandular  forma- 
tion, was  present  in  eight  species. 

In  Ophidia  and  Chelonia  there  was  a  total  absence  of  the 
parietal  eye  and  structures  pertaining  thereto  in  all  of  the  fifteen 
species  examined.  In  nine  species  of  ophidians  the  pineal 
organ  was  represented  in  nine  instances  by  a  definitely  glandular 
proximal  portion,  the  epiphysis  proper  or  corpus  pineale.  This 
gland  seems  to  contribute  its  secretion  to  the  ventricles,  but 
may  also  be  of  the  blood- vascular  type  as  well.  In  Chelonia 
there  is  evidence  that  the  pineal  organ  which  appears  as  the 
proximal  portion  of  that  structure  may  also  be  glandular  in 
nature.  The  absence  of  the  parietal  eye  elements  as  well  as  the 
pineal  organ  has  already  been  mentioned  in  Crocodilia. 

It  is  evident  from  this  summary  that  only  the  proximal  por- 
tion of  the  pineal  organ  persists  in  the  more  modern  reptiles, 
while  the  parapineal  element  as  well  as  the  end- vesicle  and  stalk 
of  the  pineal  organ,  have  entirely  disappeared. 

7.    Comparative  Anatomy  and  Histology  of  the  Epiphyseal  Complex 

in  Birds 

As  in  ophidians,  the  only  element  of  the  epiphyseal  complex 
which  persists  in  birds  is  the  proximal  portion  of  the  pineal 
organ.  This  presents  itself  as  the  epiphysis  or  corpus  pineale. 


THE    PINEAL    BODY 


149 


In  form  the  avian  epiphysis  is  conical  or  cylindrical,  sometimes 
being  flattened  by  the  approximation  of  the  cerebellum  and 
cerebral  hemispheres.  Its  size  varies  considerably  in  different 


Fig.  73    The  pineal  region  in  Gallus  domesticus,  according  to  Studnicka,  1896. 
Ds.,  dorsal  sac;  Ch.,  commissura  habenularis;  R.,  recessus  pinealis;  St.,  pineal 
stalk;  Ep.,  pineal  body;  Cp.,  commissura  posterior. 

species,  but  the  following  figures  give  a  general   idea   of   the 
dimensions. 

In  Meleagris  gallopavo 5  mm.  long  by  2.5  mm.  thick  • 

In  Gallus  domesticus 2.5  mm.  long  by  1.5  mm.  thick 

In  Strix..  6  mm.  long 


150  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

It  is  situated  close  to  the  roof  of  the  interbrain,  its  long  axis 
being  as  a  rule,  perpendicular  to  the  latter.  In  no  instance  does 
it  approach  or  come  in  contact  with  the  inner  surface  of  the 
skull. 

The  histology  of  the  structure  discloses  several  different 
forms  which  the  organ  may  assume.  Studnicka  ('05), 391  distin- 
guishes three  distinct  types:  1)  A  long  sac  with  thick  walls  con- 
taining many  follicles.  Such  an  organ  is  found  in  Passer — Gage 
('95). 136  2)  A  solid  body  with  communicating  or  independent 
acini  which  connect  with  the  lumen  of  the  pineal  body  by  means 
of  a  still  potent  canal.  Between  the  follicles  are  many  blood 
vessels  and  much  connective  tissue.  The  stalk  is  solid  as  in 
Meleagris  gallopavo — Mihalkovicz  (77). 275  3)  A  solid  organ  in 
which  there  are  solid,  blind  acini  instead  of  hollow  follicles. 
These  acini  make  up  solid  lobules. 

In  brief,  these  three  types  may  be  termed,  1)  saccular;  2) 
follicular  or  acinal,  and,  3)  solid.  There  are  a  number  of 
transitional  forms  in  addition  to  those  already  mentioned. 

Funkquist133  in  1912  describes  two  morphogenetic  types  in 
birds. 

1.  The  organ  has  a  simple  tubular  character  which,  during 
growth,  shows  a  thickening  of  its  walls  and  a  general  enlarge- 
ment.    In  some  cases  the  organ  is  solid  except  at  its  base  where 
it  retains  a  cavity,  the  recessus  pinealis. 

2.  In  this  type  the  organ  has  a  tubular  character,  in  many 
instances  retaining  its  connection  with  the  original  pineal  evagi- 
nation  and  in  others  being  cut   off  from   it.     These   bud-like 
tubular  processes  resemble  tubuli  of  the  dorsal  sac.     The  pineal 
organ  has  its  original  anlage  in  an  epithelial  structure.     Later, 
development  causes  a  transition  into  neuroglia  tissue  in  much 
the  same  way  as  the  transition  occurs  in  the  central  nervous 
system.     In  some  cases   (canary  and  turkey)   the  acinus-for- 
mation, giving  rise  to  simple  pineal  tubules,  persists,  while  in 
other  instances  these  acini  are  more  or  less  obliterated. 

Two  types  of  cells  may  be  identified,  according  to  Funkquist, 
namely,  large  epithelial  cells  with  clear  protoplasm  and  small 
darkly  staining  cells. 


THE    PINEAL  BODY 


151 


Fig.  74.     The  pineal  body  in  Coccothraustes  vulgaris,  according  to  Studnicka, 
1896. 


152 


FREDERICK    TlLNEY   AND    LUTHER   F.    WARREN 


Galeotti140  in   1896  also  recognized  two  types  of  cells,  i.e., 
radially  arranged,  cylindrical  cells  which  bound  the  lumen  of 


Fig.  75     The  pineal  body  in  Meleagris  gallopavo,  according  to  Studnicka,  1896. 

the  organ  and  small  cells  between  the  larger  ones.  In  the  large, 
cylindrical  cells,  Galeotti  found  hyaline  masses  which  he  con- 
sidered a  secretory  product  ultimately  delivered  to  the  lumen  of 


THE    PINEAL    BODY 


153 


the  acini.  Studnicka391  regarded  these  cells  as  ependymal  in 
type  just  as  in  the  lower  vertebrates,  but  found  no  sensory  cells. 
In  addition  to  the  ependymal  elements  there  were  neuroglia 
cells,  and  Studnicka  in  Meleagris  also  observed  some  very  large 
cells  with  clear  cytoplasm  scattered  among  the  other  groups. 
There  may  be  ganglionic  cells,  as  in  Acipenser.  No  nerve  fibers 
were  observed.  The  epiphysis  contains  many  isolated  cells  and 
a  secretion  derived  apparently  from  the  ependymal  cells.  No 
pigment  was  observed. 


Fig.  76  Section  of  the  pineal  body  of  Meleagris  gallopavo,  showing  follicles, 
.according  to  Studnicka,  1896. 

The  stalk  of  the  epiphysis,  which  is  of  course  in  no  sense 
homologous  Vith  the  stalk  of  the  pineal  organ,  being  a  secondary 
character  of  the  epiphysis,  is  usually  short  and  contains  the 
recessus  pinealis.  In  some  instances,  however,  it  is  solid.  No 
nerve  fibers  have  been  observed  in  it,  so  that  the  organ  has  no 
neural  connection  with  the  brain.  The  epiphysis,  including  its 
stalk  or  peduncle,  is  enclosed  within  a  sheath  of  pia  mater  and 
.arachnoid. 


154  FREDERICK    TILNEY   AND    LUTHER   F.    WARREN 

Klinckowstroem206  in  1892  has  shown  in  certain  aquatic  birds 
during  embryonic  stages,  a  very  early  appearing,  peculiarly 
pigmented  spot  on  the  head.  This  he  found  in  twelve  out  of 
two  hundred  embryos  of  Sterna  hirundo,  Larus  canus,  Larus 
marinus,  Larus  glaucus,  and  Anser  brachyrhynchus.  In  adults 
of  these  forms  no  such  spot  exists.  There  is  little  evidence  to 
indicate  the  tendency  to  the  formation  of  a  parietal  foramen. 

Dexter  ('02) 90  observed  in  Gallus  domesticus  that  the  para- 
physis  is  an  appendix  of  the  paraphyseal  arch,  developed  from 
the  brain  wall.  He  believes  it  to  be  glandular  in  character. 
In  the  adult  of  this  form  it  is  composed  of  a  modified  ectodermic 
tissue.  In  the  younger  stages  its  walls  are  thin  and  its  cavity 
is  large,  but  in  the  adult  chicken  or  hen  the  reverse  is  true.  It  is 
oval  in  shape  and  lies  nearly  parallel  with  the  longitudinal  axis 
of  the  cavity  of  the  forebrain.  It  is  a  constant  structure,  and 
Dexter  has  identified  it  time  and  again  in  the  embryo,  in  the 
chicken,  and  finally  in  the  full-grown  fowl.  Its  position  is  very 
characteristic.  The  paraphysis  is  situated  immediately  dorsad 
to  the  foramen  of  Munro  and  anterior  to  the  prominent  fold  of 
the  chorioid  plexus  which  must  morphologically  correspond  to 
the  velum  transversum. 

Differences  observed  in  the  epiphyseal  complex  in  the  various 
species  of  birds  already  investigated.  . 

1.  Gallus  domesticus.    Stieda  ('69)  ;376  Dexter  ('02)  ;90  Galeotti 
('96).14°     It   was   observed  in  this  form  that  the  epiphysis  is 
follicular  in  structure  and  glandular  in  character. 

2.  Meleagris  gallopavo.     Mihalkovicz   ('77)275   observed    that 
the  epiphysis  is  follicular  in  this  form. 

3.  Sterna  hirundo.     Klinckowstroem  ('92) 206  found  remains  of 
the  parietal  spot  in  the  embryo. 

4.  Anas  domesticata.     Klinckowstroem  ('92). 206     In  this  form 
the  author  observed  that  the  epiphysis  is  follicular. 

5.  Apteryz.     Parker  ('92). 301     The  epiphysis  in  this  form  is 
usually  anteflexed,  although  in  some  instances  it  is  dorsiflexed. 

6.  Perdix  cinerea.     Studnicka  (96). 386     The  epiphysis  in  this 
species  is  follicular. 

7.  Strix  flammea.     Studnicka  ('96). 386     In  this  form  the  epi- 
physis is  partly  solid  and  partly  follicular. 


THE    PINEAL   BODY  155 

8.  Lanius  excubitor.     Studnicka  ('96). 386    In  this  species  the 
epiphysis  is  saccular. 

9.  Turdus  pilaris.     Studnicka  ('96). 386    The  epiphysis  is  follic- 
ular  in  this  form. 

10.  Coccothraustes    vulgaris.       Studnicka     ('96). 386     In    this 
species  the  epiphysis  is  hollow  and  saccular  in  its  entire  extent. 

11.  Passer    domesiicus.      Gage    ('95). 136     The    epiphysis    is 
hollow  and  saccular  in  this  form. 

In  birds,  as  in  ophidians,  the  evidence  of  the  glandular  nature 
of  the  epiphysis  is  pronounced.  Every  form  examined  yields 
many  suggestive  indications  that  the  pineal  body  in  birds  is  a 
glandular  organ.  The  element  pertaining  to  the  parietal  eye 
has  not  been  observed  in  the  avian  forms  examined  and  the 
epiphysis  is  evidently  the  highly  specialized  proximal  portion  of 
the  pineal  organ.  The  stalk  and  end- vesicle  have  disappeared. 
The  element  referred  to  in  birds  as  the  stalk  is  something  entirely 
different  from  that  portion  of  the  lower  forms  which  connects 
the  proximal  portion  and  the  end-vesicle.  The  avian  stalk  is  a 
secondary  development  consequent  upon  the  marked  enlarge- 
ment and  solidification  of  the  proximal  portion.  During  this 
process  the  pineal  body  tends  to  move  slightly  away  from  the 
roof,  and  in  so  doing  produces  an  elongation  in  the  originally 
constricted  area  which  connects  the  epiphysis  with  the  roof  of 
the  interbrain.  This,  in  contradistinction  to  the  stalk  of  the 
end- vesicle,  is  the  stalk  or  peduncle  of  the  epiphysis.  The  pineal 
recess  contained  within  this  peduncle  is  not  entirely  homologous 
with  the  pineal  recess  of  the  lower  forms,  for  in  the  latter  in- 
stances the  recess  extends  into  the  proximal  portion  its  entire 
length,  while  in  birds  it  is  restricted  to  the  peduncle. 

8.    Comparative  anatomy  and  histology  of  the  epiphyseal  complex 

in  mammals 

In  mammals  the  only  element  of  the  epiphyseal  complex 
which  persists  is  the  proximal  portion  of  the  pineal  organ.  In 
but  a  single  instance  thus  far  recorded  is  there  evidence  of  the 
parapineal  element,  i.e.,  Cutore's74  observation  of  a  small  anterior 


156  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

protuberance  in  front  of  the  epiphysis  in  the  new-born  Bos 
taurus.  As  a  rule,  the  proximal  portion  is  solid  in  the  greater 
part  of  its  extent  and  attached  by  a  more  or  less  constricted 
portion  to  the  roof  of  the  interbrain.  This  part  of  the  epiphysis, 
sometimes  referred  to  as  the  stalk,  is  not  to  be  confused  with  the 
stalk  of  the  lower  vertebrates  which,  together  with  the  end- 
vesicle,  fails  to  develop  in  mammals.  The  mammalian  stalk  is 
more  properly  designated  the  pineal  peduncle.  The  solid  por- 
tion of  the  epiphysis  is  regarded  by  many  as  a  glandular  struc- 
ture, and  hence  the  term  pineal  gland.  In  mammals  the  follow- 
ing parts  may  be  defined:  The  epiphysis  or  pineal  body  which 
consists  of  1)  the  pineal  gland  and  2)  the  pineal  peduncle.  In 
the  latter  there  is  a  recess  of  greater  or  less  extent,  the  pineal 
recess.  The  peduncle  consists  in  a  large  part  of  nerve  fibers, 
while  the  pineal  gland  comprises  several  different  constituents. 
In  man  the  peduncle  becomes  so  specialized  in  the  nerve  fibers 
which  enter  it  as  to  constitute,  according  to  some  authorities, 
distinct  peduncular  bundles  or  epiphyseal  peduncles. 

The  form  of  the  pineal  body  in  mammals  varies  considerably. 
It  is  for  the  most  part  cone-shaped ;  it  may  be  long  or  relatively 
short.  In  marsupials  it  is  round  or  pyriform.  In  rodents  it  is, 
according  to  Flesch,121  more  or  less  cylindrical,  or,  as  Cutore76 
states,  cylindricoconical.  In  the  pig,  d'Erchia109  describes  it  as 
spindle-shaped.  In  carnivores  and  primates  the  organ  is  gen- 
erally conical  or  oval.  According  to  Schwalbe  ('81), 348  it  is  a 
dorsoventrally  flattened  globule.  In  the  primates  the  peduncle 
is  paired,  with  the  exception  of  Troglodytes  niger,  in  which, 
according  to  M  oiler  ('90), 279  the  epiphysis  is  kidney-shaped  and 
connected  with  the  brain  by  means  of  a  single  unpaired  stalk 
4  mm.  in  length.  The  epiphysis  in  most  mammals  is  dorsiflexed 
so  that  its  free  extremity  is  directed  toward  the  cerebellum.  It 
thus  presents  a  ventral  surface  in  relation  with  the  midbrain, 
a  dorsal  surface  usually  in  relation  with  the  corpus  callosum 
(although  there  are  certain  exceptions  to  this  statement),  a 
base  related  to  the  roof  of  the  interbrain,  and  an  apex.  The 
dorsal  surface  is  in  contact  with  a  reduplication  of  the  dorsal 
sac  known  as  the  lamina  superior  pediculorum  and  also  with 


THE    PINEAL   BODY 


157 


the  remnant  of  the  pars  intercalaris  anterior  forming  the  lamina 
inferior.  These  two  laminae  form  the  walls  of  a  cul-de-sac,  the 
suprapineal  recess.  The  small  space  bounded  by  the  pineal 
peduncle  is  the  pineal  recess. 

In  regard  to  its  relation  to  the  corpus  callosum,  Cutore  ('10) 76 
states  that  there  are  three  varieties  of  the  pineal  body  in  mam- 
mals, i.e.,  1)  subcallosal,  as  in  marsupials,  some  artiodactyla, 
insectivora,  carnivora,  and  primates;  2)  retrocallosal,  as  in 
most  artiodactyla  and  perissodactyla ;  3)  supracallosal,  as  in 
rodents.  Cutore  ('10)76  gives  the  following  figures  indicating 
the  relative  weight  of  the  pineal  body  to  the  brain  and  also 
the  pineal  index: 


ANIMAL 

WEIGHT  OP  BRAIN 

WEIGHT  OF 
EPIPHYSIS 

PINEAL  INDEX 

Sheep 

grams 

480  00 

grams 

0  350 

0    070 

Pig... 

140  00 

0  040 

0  020 

Goat 

119  80 

0  075 

0  060 

Horse  

512  00 

0  440 

0  080 

Ass 

420  00 

0  520 

0  100 

Mule  

430  00 

0  860 

0.200 

Rabbit... 

8  46 

0  010 

0.100 

Rat  

1  86 

0.002 

0.100 

Dog.. 

85  20 

0  080 

0.005 

Man  

1300  00 

0.220 

0.010 

The  following  tables  give  the  diameters  of  the  pineal  body  in 
man,  according  to  several  different  observers,  and  also  the 
differences  at  different  periods  of  development  as  reported  by 
Cutore:76 

Diameter  of  the  pineal  body  in  man  in  millimeters 


HENLE 

SCHWALBE 

LORD 

TESTUT 

ROMITI 

CHARPY 

CUTORE 

Longitudinal  

8 

12 

5-9 

7-8 

12 

10-12 

9-10 

Transverse 

6 

8 

3-8 

4-6 

8 

5-8 

5-7 

Anteroposterior  — 

4 

2-4 

4 

5 

4-5 

158 


FREDERICK   TILNEY   AND   LUTHER   F.    WARREN 


AGE 

SEX 

WEIGHT  OF 
BODY 

LENGTH  OF 
BODY 

ANTEROPOSTER- 
IOR  DIAMETER 
OF  BRAIN 

TRANSVERSE 
DIAMETER 
OF  BRAIN 

WEIGHT  OF 
BRAIN 

WEIGHT  OF 
HYPOPHYSIS 

WEIGHT  OF 
PINEAL  BODY 

Newborn 

Female 

grams 

2,322 

cm. 

49    5 

cm. 

10  0 

cm. 
8   6 

grams 

340 

grams 

0  032 

grams 
0  007 

8  days  

Female 

3,030 

50.0 

11.5 

8.8 

395 

0.100 

0  010 

1  month 

Female 

2,207 

52  0 

11  5 

9  4 

470 

0  100 

0  040 

3  months  
6  months  

Male 
Male 

3,700 
5,700 

63.0 
67.0 

13.8 
14.9 

11.4 
10  8 

762 
793 

0.110 
0  115 

0.035 
0  053 

10  months 

Female 

5,972 

73  0 

15  0 

12  0 

836 

0  160 

0  045 

13  months  
15  months  

Female 
Male 

6,390 
6,550 

68.0 
73  0 

15.0 
17  0 

12.0 
12  5 

795 

872 

0.140 
0  170 

0.060 
0  025 

15  months 

Male 

4,248 

73  0 

14  4 

11  0 

507 

0  120 

0  080 

18  months  

Female 

6,200 

73.5 

15.8 

12.5 

905 

0.160 

0  050 

20  months 

Female 

6,722 

74  0 

15  3 

11  3 

710 

0  180 

0  060 

3  years,  3  months  
3  years,  6  months.  .  .  . 
4  years 

Male 
Male 
Female 

5,625 

8,208 

80.0 
84.0 
91  0 

16.1 
15.9 
16  5 

12.0 
12.9 
11  8 

990 
1,000 
1,075 

0.192 
0.200 
0  190 

0.093 
0.050 
0  070 

9  years  

Male 

115  0 

17.7 

14.3 

1,100 

0.250 

0  100 

11  years 

Male 

120  0 

17  2 

13  5 

1,257 

0  400 

0  120 

13  years  

Female 

130.0 

16.7 

13.1 

1,219 

0.340 

0.170 

18  years.  . 

Male 

142  0 

16  7 

13  2 

1,200 

0  310 

0  125 

19  years  

Female 

150.0 

17.5 

13.1 

1,193 

0.320 

0.060 

22  years  

Female 

165  0 

18.0 

13.3 

1,237 

0.690 

0  070 

23  years 

Male 

162  0 

16  9 

12  5 

1,162 

0  780 

0  120 

24  years  

Male 

163.0 

17.9 

13.6 

1,300 

0.440 

0.220 

60  years. 

Female 

152  0 

17  2 

14  0 

1,273 

0.440 

0  100 

70  years 

Female 

147  0 

16  9 

13  0 

1  000 

0  650 

0  140 

70  years  

Female 

149.0 

17.2 

13.0 

1,102 

0.420 

0.150 

In  the  development  of  the  pineal  organ  in  all  vertebrates, 
only  two  of  the  germ  layers  play  a  part,  i.e.,  the  ectoderm  and 
the  mesoderm.  It  is  advantageous,  therefore,  in  considering  the 
histological  character  of  the  pineal  body,  concerning  which  there 
is  much  difference  of  opinion,  to  discuss  the  ectodermogenic 
and  mesodermogenic  elements  entering  into  that  body.  Of  the 
elements  derived  from  the  ectoderm  the  following  have  been 
observed:  1)  parenchymal  cells,  2)  ependymal  cells,  3)  neuroglial 
cells,  4)  ganglionic  cells,  and  5)  nerve  fibers.  The  following  ele- 
ments derived  from  the  mesoderm  have  been  described :  1)  con- 
nective tissue  cells,  2)  connective  tissue  trabeculae,  3)  blood 


THE    PINEAL    BODY  159 

vessels,  4)  certain  cells  called  muscle  or  myoid  cells,  5)  lympho- 
cytes, and  6)  lymphoid  reticulum. 

Hollard188  in  1837  regarded  the  epiphysis  as  a  glandular  struc- 
ture with  nerve  fibers  in  its  peduncle  only.  Valentin403  in  1843 
believed  that  the  pineal  body  possessed  a  parenchyma  which 
was  something  entirely  different  from  the  gray  matter  of  the 
brain.  He  observed  certain  'nuclear  formations '  which  had  a 
striking  resemblance  to  the  tissue  of  the  pituitary  gland.  Kolli- 
ker210  in  1850  described  the  epiphysis  in  mammals  as  consisting 
of  small,  round  cells,  multipolar  nerve  cells  and  compact  bundles 
of  nerve  fibers.  But  it  is  to  Faivre114  in  1855  that  we  are 
indebted  for  the  first  extensive  study  in  the  comparative  his- 
tology of  the  epiphysis.  Faivre  investigated  microscopically 
the  pineal  body  of  man,  horse,  guinea-pig,  dog,  ox,  rabbit,  and 
pig.  He  recognized  three  elements  in  the  human  pineal  body, 
i.e.,  1)  a  fibro vascular  envelope,  2)  a  globular  parenchyma,  and 
3)  acervulus  cerebri.  Faivre's  observation  was  in  accord  with 
Valentin's,403  that  the  pineal  body  differs  essentially  from  the 
brain.  He  concludes  that  the  parenchyma  is  made  up  largely 
of  those  globules  which  were  nuclei  of  large  elliptical  cells  in  the 
organ.  He  seems  to  have  been  the  first  to  recognize  that  these 
cells  contained  granules  and  also  that  the  parenchymal  cells 
were  smaller  in  the  child  than  in  the  adult.  Clarke69  in  1860 
found  nerve  fibers,  nuclei  and  brain  sand,  but  no  nerve  cells. 
These  elements  were  arranged  in  a  reticular  structure  which 
resembled  the  olfactory  mucous  membrane.  Luys253  in  1865 
considered  the  organ  as  a  structure  composed  of  nerve  cells 
and  fibers,  in  general,  analogous  to  the  mammillary  bodies. 
Leydig232  in  1868  states  that  the  pineal  body  in  the  mouse 
resembles  the  pituitary  gland  in  reptiles  with  certain  small 
differences.  Frey  ('67) 131  observed  in  adults  multipolar  gan- 
glionic  cells,  rounded  cells  without  prolongations  and  isolated 
nerve  tubes.  Meynert  (77)'271  asserts  that  the  parallelism 
between  the  pituitary  body  and  the  epiphysis  is  a  mistaken 
idea.  The  pineal  body  should  be  considered  a  ganglionic  deriva- 
tive of  the  tegmentum.  It  contains  two  types  of  cells,  one 
having  a  diameter  of  15  micromillimeters,  the  others  6  micro- 


160  FREDERICK   TILNEY   AND    LUTHER    F.    WARREN 

millimeters  in  diameter.  It  differs  from  other  ganglia  only  in 
the  fact  that  the  cells  are  much  closer  together.  Krause  ('68)219 
described  nerve  fibers  in  the  epiphyisis  having  a  double  contour. 
Stieda  ('69)376  observed  anastomosing  processes  of  cytoplasm 
with  nuclei  in  a  reticulum.  Bizzozerp  (7 1)32  found  two  distinct 
elements  in  the  organ,  namely,  stroma  consisting  of  prolongations 
of  the  capsule  and  a  definite  parenchyma.  In  this  latter  were 
two  types  of  cells.  In  the  larger  of  these  the  cytoplasm  con- 
tained granules.  He  noted  that  the  pineal  gland  in  the  new- 
born and  in  the  infant  contains  the  same  elements  as  in  the 
adult.  The  only  difference  is  in  the  fact  that  the  smaller  ele- 
ments have  a  few  branches  while  the  larger  cells  have  none. 
The  cells  are  arranged  in  alveoli.  Meynert  ('77) 271  concluded 
that  the  epiphysis  was  a  nerve  ganglion.  Hagemann  (72) 164 
found  two  types  of  epithelial  cells,  namely,  round  cells  and 
fusiform  cells  which  are  bipolar  and  multipolar  nerve  cells. 
The  pineal  body,  in  his  opinion,  is  a  combination  of  epithelial 
cells  and  nerve  cells.  Cruveilhier  (77) 73  found  in  the  epiphysis 
pale,  round  cells,  small  nerve  cells,  large  multipolar  cells,  and 
calcareous  concretions.  Mihalkovicz  (77) 275  concluded  that  the 
pineal  cells  were  not  lymphatic  corpuscles,  but  resembled  the 
cells  in  the  lining  of  the  cerebral  ventricles.  Schwalbe  ('8 1)348 
considered  the  pineal  cells  to  be  modified  epithelium  with  a 
striking  resemblance  to  lymphatic  corpuscles.  Cionini  ('85- 
'86)66>  67  first  demonstrated  the  presence  of  neuroglial  elements,, 
the  nerve  fibers  observed  belonging  to  the  blood  vessels.  Dark- 
schewitsch  ('86) 79  refutes  the  idea  that  the  pineal  body  is  nothing 
more  than  a  'simple  gland.'  By  the  Weigert  method  he  found 
the  nerve  fibers  from  the  following  sources:  1)  internal  capsule, 
2)  striae  medullares,  3)  Meynert's  bundle,  4)  optic  tract,  and 
5)  posterior  commissure.  Meynert271  and  Pawlowsky305  have 
already  noted  the  connection  between  the  posterior  commissure 
and  the  pineal  body.  Henle172B  in  1887  considered  the  pineal 
body  as  a  lymphatic  ganglion.  Its  parenchyma  consisted  of 
two  types  of  cells,  i.e.,  round  cells  resembling  lymph  corpuscles 
and  angular  cells  with  many  points. 


THE    PINEAL   BODY 


161 


Ellenberger  ('87)no  maintains  that  the  pineal  body  in  the 
horse  is  very  similar  to  a  lymphatic  gland.  It  is  highly  vascular; 
in  it  are  but  a  few  nerve  fibers  and  these  are  difficult  to  trace  to 
their  origin.  Flesch  ('88)123  studied  the  pineal  body  in  the 
horse,  pig,  dog,  bat,  and  man.  He  was  able  to  find  brain  sand 
in  man  only.  He  does  not  believe  that  the  organ  is  rudimentary, 
but  regards  it  as  an  epithelial  structure.  There  are  some  nerve 


Fig.  77  Follicles  and  parenchyma  of  pineal  body  in  man,  showing  concretion 
of  brain  sand,  according  to  Henle,  1879. 

fibers  in  it.  Its  relation  to  the  size  of  the  brain  is  not  definite. 
It  has,  in  Fleseh's  opinion,  a  physiological  action  in  mammals, 
is  very  vascular,  while  its  specific  cells  contain  pigment  granules. 
It  seems  to  be  a  secretory  organ  and  may  contain  a  heat-regulat- 
ing centre. 

Edinger  (797)104  found  the  pineal  body  in  the  higher  mammals 
to  be  formed  of  neuroglia  cells.  True  nerve  elements  are 
absent.  Chauveau  ('85) 64  observed  groups  of  polyhedral  cells 


MEMOIR  NO.  9 


162  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

separated  by  connective-tissue  trabeculae.  He  also  mentions 
calcareous  deposits  in  domestic  animals.  Mingazzini  ('89) 276 
believes  the  pineal  elements  resemble  lymphatic  corpuscles. 
Soury  ('99)365  found  a  substance  like  adenoid  tissue  filling  the 
spaces  of  a  fine  network.  Weigert  ('95)419  describes  the  pineal 
body,  especially  its  ventral  portion,  as  composed  of  a  thick 
layer  of  neuroglia  fibers  of  such  a  specific  nature  that  the  like  of 
it  is  not  found  elsewhere  in  the  central  nervous  system.  The 
cells  are  very  numerous  and  traversed  by  many  fibers.  Cajal 
('95) 53  found  sympathetic  fibers  entering  the  pineal  body  with 
the  vessels.  These  fibers  form  a  rich  interstitial  plexus.  The 
fibers  surround  but  do  not  penetrate  the  cytoplasm  of  the 
glandular  cells.  Galeotti  ('96-'97)14°  makes  the  claim  that 
the  pineal  body  is  a  secretory  organ  and  believes  there  is  evi- 
dence of  this  in  many  vertebrates  besides  mammals.  The  pineal 
cells  elaborate  a  pigment  in  addition  to  their  secretory  product. 
He  recognized  nerve  cells  which  are  in  relation  with  the  superior 
and  posterior  commissures,  ependymal  cells  constituting  the 
middle  portion  of  the  body,  in  relation  with  the  pineal  recess, 
and  epithelial  cells  which  constitute  the  epiphyseal  tube  in  some 
animals  and  the  epiphysis  in  mammals.  Lord  ('99)249  described 
the  parenchyma  of  the  human  pineal  body  as  formed  of  small 
stellate  cells  resembling  those  of  adenoid  tissue  together  with 
other  paler  cells  of  variable  size.  Nicolas  ('00)283B  found  striated 
muscle  cells  in  the  distal  portion  of  the  pineal  body  in  the  ox  and 
calf.  Dimitrova  ('01), 92  a  pupil  of  Nicolas',  studied  the  pineal 
body  in  mammals,  young  and  old,  including  man,  ox,  calf,  sheep, 
horse,  dog,  and  cat.  She  maintains  that  Nicolas'  observations 
were  confirmed  by  her  studies  and  that  striped  muscle  cells  do 
occur  in  the  pineal  body  of  the  ox  and  calf.  In  her  opinion, 
the  essential  constituent  of  the  epiphysis  in  mammals  is  neuroglia 
and  she  concludes  that  in  addition  to  the  essential  neuroglial 
nature  of  the  pineal  body  there  exists  in  the  ox,  calf,  sheep,  and 
dog  certain  cavities  which  resemble  thyroid  vesicles  or  the 
anterior  pituitary  lobe.  In  young  cats  some  cells  which  are 
independent  of  the  neuroglia  seem  to  resemble  the  elements 
described  by  Cajal54  and  Retzius331A  as  sympathetic'  and  may  be 


THE    PINEAL   BODY 


163 


Fig.  78     A  striated  muscle  fiber  from  the  pineal  body  of  Bos  taurus,  according 
to  Dimitrova,  1901. 


164 


FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 


neuroglia  cells  in  process  of  development.  Favaro  ('04) 118 
gives  the  following  conclusions  of  his  studies  by  means  of  the 
Weigert  method  upon  many  mammals,  including  artiodactyla, 
peris sodacty la,  rodent ia,  insectivora,  carnivora,  and  primates. 
Fibers  found  in  relation  to  the  pineal  body  are : 
1.  Prepineal  fibers: 

a)  Transverse  commissural 

6)  Oblique  commissural 


Fig.  79    Cells  and  fibers  in  the  pineal  body  of  Bos  taurus  (Weigert's  method), 
according  to  Dimitrova,  1901. 

2.  Fibrae  seu  fasciculus  prepinealis. 

3.  Pineal  fibers: 

a)  Superior  transverse  commissural  fibers 
6)  Superior  oblique  commissural  fibers 

c)  Posterior  transverse  commissural  fibers 

d)  Diagonal  commissural  fibers 

e)  Superior  and  posterior  fibrae  propriae 

Anglade    and    Ducos    ('08-09) 5    found    neuroglia    constantly 
present  in  the  human  pineal  body  but  also  alveoli-formed  cells 


THE    PINEAL   BODY  165 

of  a  different  character.  Sarteschi  ('10)345  found  that,  as  com- 
pared with  the  adult  animals,  the  epiphysis  in  the  young  rabbit 
and  guinea-pig  was  distinctly  more  glandular  and  in  this  regard 
similar  to  the  organ  in  birds.  In  the  course  of  growth  certain 
regressive  changes  occur.  Neuroglia  and  glandular  cells  were 
present  in  all  of  the  forms  which  Sarteschi  studied.  Constantini 
('10) 71  studied  the  pineal  body  of  the  ox,  horse,  and  man.  He 
describes  two  types  of  epithelial  cells,  i.e.,  1)  acidophiles  and 
2)  basophiles.  He  concludes  that  the  pineal  body  in  mammals  is 
an  organ  of  internal  secretion.  Cutore  ('10),76  on  the  basis  of  a 
study  of  many  different  mammals,  concludes  that  there  are  the 
following  histological  elements  in  the  pineal  body:  1)  Epithelial 
cells  containing  granules  and  delimiting  the  cavities  of  tubules 
or  acini.  2)  Lymphatic  elements  very  numerous  in  larger 
mammals  and  massed  about  the  epipthelial  cells.  3)  Connec- 
tive tissue  forming  trabeculae  producing  an  apparent  trabecula- 
tion  of  the  parenchyma.  This  connective  tissue  contains  elastic 
fibers,  blood  vessels,  lymph  spaces,  and  pigment  cells  probably 
belonging  to  the  category  of  mast  cells.  Some  of  the  latter 
cells  give  evidence  of  a  process  of  fragmentation.  4)  Cal- 
careous concretions  of  calcium  carbonate  and  phosphate.  These 
latter  are  sometimes  found  as  inclusions  in  the  cytoplasm  or  in 
the  meshes  of  the  connective  tissue.  Cutore  believes  it  to  be  an 
organ  of  such  complex  structure,  constituted  of  neuroglia, 
epithelium,  lymphatic  and  connective  tissues,  so  arranged  as  to 
form  acini  and  so  highly  vascular,  that  it  cannot  be  considered 
to  be  in  a  state  of  regression  as  is  claimed  by  Moller,278  Charpy,62 
Dejerine,85  and  others.  Indeed,  the  highly  specialized  and  char- 
acteristic structure  of  the  pineal  body  is  sufficient  justification 
to  attribute  to  it  an  internal  secretory  function.  Galasescu 
and  Urechia  (710)137  found  in  the  vicinity  of  some  of  the  blood 
vessels  round  and  oval  cells  with  deeply  staining  nuclei  situated 
centrally  in  a  cytoplasm  which  stains  with  acid  stains,  e.g., 
eosin  and  fuchsin.  The  cytoplasm  is  granular  and  well  demar- 
cated. These  acidophiles  resemble  those  seen  in  the  para- 
thyroids. The  authors  propose  to  term  these  cells  the  'para- 
vascular  acidophiles/  They  believe  these  elements  play  a  defi- 
nite part  in  the  internal  secretion  of  the  pineal  body. 


166  FREDERICK    TILNEY   AND    LUTHER   F.    WARREN 

A 

c  ^ 


B 


Fig.  80    Neuroglia  cells  in  the  human  pineal  body  (Golgi's  method), 
cording  to  Cionini,  1889;  B,  according  to  Dimitrova,  1901. 


A,  ac- 


THE    PINEAL    BODY 


167 


Krabbe  (711)217  studied  one  hundred  human  pineal  bodies, 
both  male  and  female,  from  birth  to  seven  years  of  age  and  from 
fourteen  years  to  ninety-two  years.  There  was  a  gap  in  his 
subjects  between  the  ages  of  seven  and  fourteen  years.  He 
found  two  types  of  cells  in  the  epiphysis:  1)  special  pineal  cells 
and  2)  neuroglia  cells.  He  thinks  the  granules  in  the  cells  leave 
the  protoplasm,  traverse  the  intercellular  space  to  enter  the 
blood,  lymph,  or  cerebrospinal  fluid,  Krabbe  does  not  agree 
with  Dimitrova92  that  the  fundamental  element  of  the  pineal 


Fig.  81     Cells  with  granular  protoplasm  in  the  pineal  body  of  Bos  taurus  (Wei- 
gert's  method),  according  to  Dimitrova,  1901. 


body  is  neuroglia,  for  he  considers  her  criteria  in  distinguishing 
neuroglia  insufficient.  He  himself  never  observed  muscle  fibers 
in  any  of  the  forms  which  he  has  studied.  Krabbe  concludes 
that  the  epiphysis  in  man  shows  certain  signs  of  involution, 
as,  for  example,  concretions,  hyperplasia  of  connective  tissue, 
neuroglial  plaques  with  cysts,  and  the  presence  of  cells  in  a  state 
of  disintegration.  The  involution  begins  at  seven  years  of 
age,  but  even  in  the  adult  the  pineal  body  shows  signs  of  active 
function.  The  secretory  process  is  manifest  in  the  following 


168  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

manner:  1)  basophilic  granules  in  the  nuclei;  2)  the  latter  evac- 
uated into  cytoplasm.  This  process  goes  on  during  the  entire 
life  of  the  individual  even  into  old  age. 

Biondi  ('12)49  calls  attention  to  the  finding  of  Constantini71 
and  Galeotti140  of  acidophiles  in  the  pineal  body.  Biondi  made 
a  special  study  for  mitochondria  by  the  method  of  Regand. 
He  was  able  to  demonstrate  small  granules  which  he  thinks 
must  be  regarded  as  mitochondria.  This  he  cites  as  evidence 
of  the  secretory  nature  of  the  epiphysis.  He  calls  attention  to 
the  fact,  however,  that  Nageotte281  and  Mawas263  have  both 
stated  that  neuroglia  cells  also  contain  mitochondria. 

Jordan,  ('II)197  following  the  histogenesis  of  the  pineal  body 
of  the  sheep,  studied  six  stages  from  5  cm.  to  21  cm.,  also  of  the 
eight  months'  lamb,  yearling,  and  old  sheep.  He  found  no 
muscle  fibers.  Between  birth  and  the  first  year  the  pineal  body 
increases  fivefold  in  size.  In  the  fetus  there  are  blind  alveoli 
and  the  organ  is  definitely  lobulated  by  ingrowths  from  the  pia. 
Parenchymal  cells  form  these  alveoli.  Vascular  follicles  are 
abundant.  The  parenchyma  consists  of  a  more  or  less  dif- 
ferentiated ependyma.  After  the  first  year  there  are  signs  of 
local  degeneration  manifesting  themselves  as  an  increase  in  con- 
nective tissue,  neuroglia,  brain  sand,  clumps  of  pigment  granules, 
and  a  decrease  of  parenchymal  cells.  The  entire  pineal  body 
decreases  in  size  after  the  first  year.  He  concludes  that  there 
is  no  cytologic  evidence  in  favor  of  the  secretory  function  of  the 
sheep's  pineal  body.  He  points  out,  however,  that  the  general 
structure  of  the  epiphysis,  including  its  lobulation,  its  connec- 
tive tissue  framework,  its  parenchymal  follicles,  blind  alveoli, 
perivascular  lymph  spaces,  great  vascularity,  and  presence  of 
cytoplasmic  granules,  is  indicative  of  a  glandular  function  of 
internal  secretion.  He  interprets  the  cysts  which  appear  in  the 
pineal  body  and  the  melanic  cytoplasmic  granules  as  probably 
having  an  ancestral  significance.  In  Jordan's  opinion,  if  the 
pineal  body  subserves  any  important  function  at  all,  this  is 
true  only  of  the  first  eight  months  of  postnatal  life. 

Jordan198  in  the  same  year,  studying  the  pineal  body  in  the 
opossum,  states  that  the  organ  in  this  species  has  two  forms: 


THE    PINEAL   BODY 


169 


Fig.  82  Transverse  section  of  the  pineal  bod}'  in  the  rat,  according  to  Ramon 
y  CajaL  1904 

a-6,  sympathetic  nerve  fibers;  c.,  interstitial  nerve  plexus;  Bl.,  blood  vessel; 
Hm  ,  hemisphere. 


170 


FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 


Fig,  83    Histological  characters  of  the  pineal  body  in  the  sheep,  according  to 
Jordan,  1911. 


THE    PINEAL   BODY  171 

1)  long  and   tubular,   as  in  birds  and  reptiles;  2)  short  and 
cup-shaped,    resembling   particularly   that   of   carnivora.     The 
epiphysis  is  composed  of  a  syncytial  network,  in  the  meshes  of 
which  are  scattered  more  or  less  highly  differentiated  or  modified 
ependymal  cells  and  delicate  bundles  of  nerve  fibers.     In  the 
opossum  it  appears  to  be  in  a  state  of  instability.     Its  long, 
tubular  form   connects  it  phylogenetically  with  the  birds  and 
reptiles,  while  its  short,  cup-shaped  form  affiliates  it  with  the 
carnivora.     Regarding  the  function  of  the  pineal  body  in  the 
opossum,  Jordan  believes  that  his  observations  show  it  to  be 
unimportant  in  the  body  metabolism  of  mammals.     This  does 
not  necessarily  mean  that  there  is  no  specific  secretion  from 
the  organ,  but  rather  that  it  has  no  direct  or  indirect  influence 
upon  vegetative  functions. 

Nerve  fibers  in  the  mammalian  epiphysis  have  been  observed 
by  Kolliker210  in  1850,  who  appears  to  be  the  first  to  demonstrate 
these  elements.  Krause219  in  1868  recognized  the  fact  that  the 
fibers  have  a  double  contour,  and  Darkschewitsch79  in  1886 
showed  that  they  were  myelinated  nerve  fibers.  Connections 
have  been  demonstrated  to  exist  between  the  pineal  body  by 
means  of  these  fibers  with  the  following  parts:  1)  internal  capsule; 

2)  striae  medullares;  3)   Meynert's  bundle;  4)   optic  tract  by 
Darkschewitsch,  ('86) 79  and  5)  posterior  commissure  by  Meynert 
(77), 271    Pawlowsky    (74),305    Cionini    ('88), 68   Favaro,    ('04)118 
and  Cutore  ('10)  ;76  6)  commissura  habenularis  by  Kolliker  ('50)21° 
Hagemann  (72), 164  Favaro  ('04)118  and  Cutore  ('10), 76  7)  sym- 
pathetic   system,    Henle    (79),172    Cionini    ('86), 67    and    Cajal 
('04).54     Ganglion  or  nerve  cells  in  the  epiphysis  have  been 
described  by  Kolliker210  in    1850   and    Hagemann164   in    1872. 
Cajal53  in  1895  also  found  ganglion  cells  in  the  pineal  body  and 
described  two  types.     Dimitrova92   in    1901    was   able  to  find 
ganglionic  cells  in  young  cats  only. 

Pigment  has  been  found  in  the  epiphysis  of  mammals  by 
Flesch123  ('88).  Galeotti  ('96)14°  observed  pigment  particles  in 
the  cytoplasm  and  nuclei.  Dimitrova  ('01) 92  found  a  golden- 
brown  pigment  in  the  parenchymal  cells.  Cutore  ('10) 76  ob- 
served pigment  in  the  pineal  cells.  Brain  sand  has  been  described 


172  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

by  many  authors  in  a  number  of  mammals.  Haller  (1768) 165 
considered  it  pathological,  but  Soemmering's360  classical  study 
upon  the  acervulus  clearly  demonstrated  that  these  concretions 
are  normal  in  man.  Malacarne  (1795)258  found  brain  sand  in 
the  epiphysis  of  the  goat.  Wenzel  (1812)420  described  it  in  man 
as  being  of  two  varieties  according  to  its  color,  i.e.,  yellow  or 
white.  Hagemann  (72) 164  considered  it  a  normal  constituent 
of  the  adult  pineal  body  in  man.  He  also  observed  it  in  the  ox. 
Krause  ('76) 218  found  it  in  many  adult  mammals.  Flesch123 
describes  brain  sand  in  the  epiphysis  of  the  horse,  sheep,  pig, 
and  dog. 

A  parietal  foramen  has  never  been  observed  in  mammals,  but 
the  white  spot  which  frequently  appears  in  the  frontal  region  of 
the  horse's  head  has  been  suggested  as  a  vestigial  indication  of 
this  aperture  in  the  skull  seen  in  many  of  the  lower  vertebrates. 

Differences  observed  in  the  epiphyseal  complex  in  the  various 
species  of  mammals  already  investigated. 

MARSUPIALS.  1.  Macropus  giganteus.  Lotheissen  ('94).25°  In 
this  species  some  nerve  fibers  penetrate  into  the  substance  of 
the  pineal  gland.  These  come  from  the  fasciculus  retroflexus 
of  Meynert.271  They  were  not  observed  in  other  mammals. 

2.  Halmaturus  dorsalis.     Condorelli-Francaviglia   ('95). 70     In 
this  form,  because  of  the  rudimentary  corpus  callosum,  the  pineal 
body  extends  dorsad  between  the  hemispheres.     Its  length  is 
2  mm.  and  its  thickness  1.5  mm. 

3.  Didelphys  virginiana.     Jordan   ('II).198     In   the    opossum 
the  pineal  body  occurs  in  two  forms,  i.e.,  either  as  a  long  tubular 
organ  or  as  a  short,  cup-shaped  structure.     It  is  composed  of 
ependymal  cells  in  a  syncytial  network. 

ARTIODACTYLA.  1.  Bos  taurus.  Faivre  ('55)  ;114  Hagemann 
(72);i64  Chauveau  ('85)64  Nicolas  ('00);283B  Dimitrova  ('01)  ;92 
Favaro  ('04) ;117  Constantini  ('10);7lA  Cutore  ('09). 74  In  this 
species  the  pineal  body  is  cylindrico  conical.  Its  diameters  are : 

cm. 

Longitudinal 1.5 

Transverse 0.7 

Anteroposterior 0.7 


THE    PINEAL  BODY  173 

It  consists  of  large  parenchymal  cells,  neuroglia,  and  lym- 
phatic elements.  It  is  very  vascular.  Cutore  could  find  no 
muscle  cells.  Some  observers  have  found  brain  sand  in  the 
organ. 

2.  Sus  scrofa  domesticus.     Faivre  ('55), 114  Hagemann  (72) ;164 
Flesch  ('87)  ;121  Favaro  ('04)  ;118  Cutore  ('10). 76    In  this  form  the 
pineal  body  is  long  and  pointed  toward  its  distal  extremity. 
Its  diameters  are: 

CWl. 

Longitudinal 1.0 

Transverse 0.5 

Anteroposterior 0.4 

Fibers  connect  it  with  the  ganglion  habenulae  and  the  pos- 
terior commissure.  It  contains  no  concretions  and  no  pigment. 
Histologically  it  resembles  the  pineal  body  of  Bos  taurus. 

3.  Capra    hircus.     Malacarne    ('95)  ;258     Hagemann    (72)  ;164 
Staderini   ('97) ;372  Cutore   ('10).76    In  this  species  the  pineal 
body  is  relatively  short  and  conical.     Its  diameters  are: 

cm. 

Longitudinal 0.70 

Transverse 0. 55 

Anteroposterior 0.45 

Malacarne  described  brain  sand  in  the  organ.  Cutore  could 
find  neither  concretions  nor  pigment.  Fibers  connect  the  base 
of  the  epiphysis  to  the  posterior  commissure  and  habenular 
region. 

4.  Camelus  dromedarius.     Parisini.300    In  this  form  the  author 
described  concretions. 

5.  Ovis   aries.     Flesch    ("87)  ;127   Dimitrova    ('01)  ;92   Favaro 
('04)  ;118  Jordan  ('II).199     In  the  adult   of  this   species  Jordan 
describes   signs   of   degeneration,   including  hyperplasia,   brain 
sand,  clumps  of  pigment  granules,  and  a  decrease  of  parenchymal 
cells. 

PERISSODACTYLA.  1.  Equus  caballus.  Faivre  ('55)  ;114  Hage- 
mann (72)  ;164  Ellenberger  ('87)  ;110  Flesch  ('88)  ;123  Favaro  ('04)  ;118 
Cutore  ('10).76  In  this  species  the  pineal  body  is  conical.  Its 
diameters  are: 


174  FREDERICK    TILNEY   AND    LUTHER    F.    WARREN 

cm. 

Longitudinal 0.8 

Transverse 0.6 

Anteroposterior 0.5 

Nerve  fibers  are  found  in  the  base  of  the  epiphysis.  Histo- 
logically,  the  pineal  body  consists  principally  of  a  delicate  con- 
nective-tissue framework,  in  the  meshes  of  which  are  found 
lymphatic  elements.  Many  pigment  cells  are  also  found  having 
a  brownish  color  and  occupying  usually  a  perivascular  position. 
Neuroglia  and  ependymal  cells  are  also  present. 

2.  Equus  asinus.     Cutore  ('10).76     In  this  species  the  pineal 
body  is  larger  than  in  the  horse  and  its  form  is  oval.     Its  diam- 
eters are: 

cm. 

Longitudinal 1.5 

Transverse 0.6 

Anteroposterior 0.6 

Its  histology  is  much  the  same  as  that  of  the  horse.  Peri- 
vascular  pigmented  cells  are  present  in  large  numbers. 

3.  Equus  mulus.     Cutore   ('10).76     The  pineal  body  in  this 
species  is  relatively  large.     Its  diameters  are: 

cm. 

Longitudinal 1.5 

Transverse 0.6 

Anteroposterior 0.6 

It  is  conical  in  form.  Histologically,  it  consists  of  paren- 
chymal  cells  containing  pigment  granules.  In  addition,  there 
are  ependymal  cells,  neuroglia,  and  lymphatic  elements. 

4.  Elephas    indicus.     Parisini.300     In    this    animal    Parisini 
reports  the  presence  of  concretions. 

INSECTIVORA.  1.  Erinaceus  europaeus.  Cutore  ('10).76  In 
this  species  the  epiphysis  is  triangular  and  is  situated  in  the 
inter collicular  sulcus.  It  presents  a  well  developed  pineal  recess. 
Histologically,  its  elements  resemble  those  of  other  mammals, 
the  cells  being  arranged  in  acini,  not  unlike  the  cellular  forma- 
tions in  the  hypophysis. 

RODENTIA.  1.  Talpa.  Ganser  ('82). 142  In  this  form  the 
pineal  body  was  considered  an  unpaired  ganglion  habenulae. 
It  receives  fibers  from  the  thalami  and  the  posterior  commissure. 


THE    PINEAL   BODY  175 

2.  Lepus   cuniculus.     Tiedemann    ('23)  ;395   Marshall    ('61)  ;261 
Krause  ('68)  ;219  Bizzozero  ('68)  ;30  Hagemann  (72)  ;164  Mihalko- 
vicz    (77)  ;275    Edinger    ('97)  ;104    Staderini    ('97)  ;372    Neumayer 
('99)  .282  Favaro  (>Q4)  ;118  Cutore  ('10)  ;76  Sarteschi  ('10).345 

The  pineal  body  in  this  species  is  long  and  cylindrical  and  of 
such  a  shape  as  to  justify  the  ancient  term,  penis  cerebri.  Its 
diameters  are: 

cm. 

Longitudinal  ......................................................  1.0 

Transverse  ........................................................  0.3 

Anteroposterior  ....................  ...............................  0.2 

Its  histological  appearance  resembles  that  of  adenoid  tissue. 
There  are  no  pigment  cells  and  no  concretions. 

3.  Cavia  cobaya.     Faivre  ('55)  ;114  Hagemann  (72)  ;164  d'Erchia 
('96)  ;109  Staderini  ('97)  ;372  Favaro  ('04)  ;118  Cutore  ('10)  ;76  Sar- 
teschi ('10).345     In  this  species  the  pineal  body  is  similar  in  form 
to  that  of  the  rabbit.     Its  diameters  are: 

cm. 
Longitudinal  .................................................  .....  0.8 

Transverse  ........................................................  0.4 

Anteroposterior  ...................................................  0.3 

Histologically,  the  organ  resembles  that  of  the  rabbit. 
4  Mus   decumanus.      Staderini  '97  ;372    Cutore    ('10).  7G     The 
pineal  body  in  this  species  is  elongated.     Its  diameters  are: 

cm. 

Longitudinal  ......................................................  0.5 

Transverse  .........................................................  0.3 

Histologically,  it  presents  a  rich  vascularization  and  paren- 
chymal  cells  similar  to  those  of  other  rodents.  Pigment  and 
calcareous  concretions  are  absent.  Neuroglia,  nerve  fibers, 
elastic  fibers,  and  lymphatic  elements  are  also  observed. 

5.  Dasyprocta  agouti.  Sperino  and  Balli  ('09).37°  In  this 
species  the  form  of  the  pineal  body  is  cylindricoconical.  Its 
appearance  is  brownish,  its  apex  is  retroflexed  so  that  the  struc- 
ture rests  in  the  intercollicular  sulcus.  Its  diameters  are  : 


Longitudinal 
Transverse.., 


176  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

CARNIVORA.  1.  Phoca  vitulina  and  Rosmarus  obesus.  Tur- 
ner ('88)  .40°  In  the  walrus  and  seal  the  pineal  body  has  a  greater 
relative  magnitude  than  in  other  mammals. 

2.  Canis   familiaris.     Tiedemann    ('23)  ;395    Faivre     ('55)  ;114 
Flesch  ('88)  ;123  Dimitrova  ('01)  ;92  Favaro  ('04)  ;118  Cutore;  ('10). 76 
In  this  species  the  pineal  body  is  conical  in  form.     It  is  relatively 
small.     Its  diameters  are: 

cm. 

Longitudinal 0.4 

Transverse : 0.3 

Anteroposterior 0.1 

Histologically,  it  consists  of  neuroglia,  nerve  fibers,  and 
parenchymal  cells  which  are  polyhedral  in  form  and  arranged 
in  acini.  Some  cells  contain  pigment  granules.  In  addition  to 
these  elements  there  are  large  cylindrical  ependymal  cells. 
There  are  no  concretions  present. 

3.  Felis    domestica.     Tilney    ('15). 396    The    pineal    body    in 
the  cat  is  even  smaller  than  in  the  dog  and  it  is  ovoid  in  form. 
Its  diameters  are: 

COT. 

Longitudinal 0 . 20 

Transverse 0. 15 

Anteroposterior 0. 10 

Histologically,  it  resembles  the  epiphysis  of  the  dog. 

4.  Felis  leo.     Parisini.300    This  author  described  concretions 
in  the  pineal  body  of  the  lion. 

PRIMATES.  1.  Troglodytes  niger.  Moller  ('90)  ;278  Marshall 
('61) ;261  Dendy  and  Nicolls  ('II).88  In  this  species  the  pineal 
gland  lies  in  a  groove  between  the  superior  colliculi  and  has  an 
unpaired  peduncle.  There  is  a  deep  pineal  recess  and  a  well 
developed  suprapineal  recess.  No  concretions  were  described 
in  this  species. 

2.  Macacus  sinicus.  Cutore  ('12). 76  In  this  species  the  di- 
mensions of  the  pineal  body  are: 

cm. 

Longitudinal 0.5 

Transverse 0.2 

Anteroposterior 0.2 


THE    PINEAL  BODY  177 

The  pineal  body  is  cylindricoconical  in  form  in  Macacus  sinicus 
and  presents  a  great  number  of  nerve  fibers. 

3.  Cercopithecus    griseus    viridis.     Cutore     ('10).76     In    this 
species  the  dimensions  of  the  pineal  body  are: 

cm. 

Longitudinal 0.3 

Transverse 0.2 

Anteroposterior 0.2 

The  pineal  body  in  this  form  is  conical  in  shape.     The  struc- 
ture of  the  organ  is  evidently  glandular. 

4.  Homo  sapiens.     A  large  number  of  observers  have  given 
their  attention  to  the  pineal  body  in  man  and  many  diverse 
opinions  have  been  expressed  concerning  it.     Cutore's76  sum- 
mary giving  the  histology  and  dimensions  of  the  pineal  body  in 
man  is  the  most  recent  and  complete  review.     The  figures  have 
already  been  cited  (p.  157).     Cutore  concludes  that  the  human 
pineal  body  develops  slowly,  retaining  even  up  to  the  time  of 
birth  its  primitive  diverticular  form.     In  the  adult,  however, 
this  organ  has  become  relatively  voluminous  and  the  original 
recess  is  much   reduced  to  form   the   ventriculus   or  recessus 
pinealis.     The  superior  or  habenular  commissure  is  small.     The 
pineal  fibers  are  limited  in  number  and  distributed  to  the  inferior 
third  of  the  organ.     In  the  disposition  of  the  parenchyma  there 
is  seen  a  distinct  tendency  for  the  cells  to  arrange  themselves 
in  circular  areas  clearly  delimiting  small  cavities  in  which  there 
appears  an  amorphous  or  crystalline  substance.     Elastic  tissue 
is  scanty,  but  pigment  cells  are  numerous  and  concretions  of 
varying  sizes  appear  in  large  numbers.     The  vascularization  is 
rich  especially  around  the  aciniform  groups  of  cells.     Neuroglia 
and  cylindrical  ependymal  cells  are  also  present.     Connective- 
tissue  processes  from  the  pia  mater  form  an  irregular  partition 
of  the  tissue  into  lobules.     Siegneur351  considers  the  pineal  body 
in  man  a  gland,  the  cells  of  which  are  of  two  types,  those  which 
are  polyhedral  with  granules  in  the  cytoplasm.     These  granules 
are  most  numerous  about  the  nucleus.     Some  of  the  cells  have 
vacuoles.     The  second  type  of  cells  are  even  larger  and  contain 
large  nuclei  which  stain  deeply  and  occupy  an  excentric  position  in 


MEMOIR  NO. 


178  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

the  protoplasm.  In  the  new-born,  lobation  of  the  gland  is  much 
more  easily  discerned  than  in  the  later  periods  of  life. 

The  histology  of  the  pineal  body  of  the  following  mammals 
has  not  heretofore  been  given,  and  as  it  seems  to  furnish  some 
details  in  the  finer  structure  of  the  organ,  the  authors  have 
considered  it  advantageous  to  include  these  original  observations 
in  this  work.  All  of  the  material  was  obtained  from  the  study 
collections  of  the  Department  of  Anatomy,  Columbia  University. 
It  includes  specimens  of  Marcopus  grayi,  Camelus  dromedarius, 
Copra  hylocrius,  Zalophus  calif ornianus,  Lepus  cuniculus,  and 
Simia  satyrus.  In  addition  to  these  species,  the  later  stages  of 
development  in  the  human  fetus  and  in  Felis  domesiica  were 
studied.  The  staining  methods  used  were  the  Van  Giesen, 
hsematoxylin-eosin,  and  Weigert's  iron  hsematoxylin.  On  ac- 
count of  the  limited  amount  of  tissue  it  was  impossible  to  do 
any  silver  impregnation  so  that  no  evidence  was  obtained  con- 
cerning the  nature  of  the  nerve  fibers  in  the  pineal  body. 

1.  Macropus  grayi.  In  this  species  the  cellular  constituents 
of  the  pineal  body  present  the  most  striking  features  of  any 
of  the  mammals  studied.  Four  types  of  cells  are  noted: 

First.  Large  cells  with  extensive  cytoplasm  and  a  large  vesicu- 
lar nucleus.  The  nuclei  of  these  cells  stain  very  deeply. 

Second.  Cells  of  a  similar  size  with  vesicular  nuclei  which 
stain  feebly. 

Third.  Smaller  cells  with  a  large  nucleus  and  a  very  small 
amount  of  cytoplasm.  The  nuclei  are  intensely  basophilic. 

Fourth.  Small  cells  with  feebly  staining  nuclei  showing  many 
granules. 

The  cells  of  these  four  varieties  arrange  themselves  in  a  more 
or  less  distinctive  manner.  The  large  epithelial  elements  of 
both  types  are  disposed  in  such  a  way  as  to  form  well-defined 
acini.  Interspersed  between  these  acinous  groups  are  more  or 
less  irregularly  convoluted  chains  or  cords  of  cells  made  up  of 
both  varieties  of  the  large  type.  The  smaller  cellular  elements 
are  scattered  among  the  cords  and  acini  in  an  irregular  manner. 
Trabeculae  of  connective  tissue  serve  to  give  the  impression  of 
lobulation  to  the  structure,  although  these  lines  of  separation 


THE    PINEAL   BODY  179 

are  irregular.  The  pineal  body  of  Macropus  is  highly  vascular. 
The  larger  vessels  follow  the  lines  of  the  connective-tissue  sep- 
tum. No  concretions  were  observed  in  any  part  of  the  pineal 
body.  The  impression  given  by  the  arrangement  and  char- 
acter of  the  cells  in  the  pineal  body  of  this  species  is  that  of  a 
glandular  structure  resembling  in  a  general  way  this  organ  in 
reptiles  and  birds  (fig.  84). 

2.  Capra  hylocrius.     In  this  animal  four  types  of  cells  may  be 
distinguished,  as  in  the  kangaroo.     Here,  however,  the  large 
elements  with  a  deeply  staining  nuclei  are  more  abdundant  and 
a  smaller  number  of  the  small  cells  with  pycnotic  nuclei  are 
observed.     The  arrangement  of  the  cells  is  typically  aciniform, 
although  there  are  areas  in  which  no  such  disposition  of  the 
cells  can  be  made  out.     These  portions  of  the  pineal  body, 
therefore,  in  which  the  acini  do  appear  stand  out  conspicuously 
in  contrast  to  the  areas  of  the  tissue  in  which  the  cellular  arrange- 
ment is  more  diffuse.     The  size  of  the  acini  varies  greatly  from 
about  10  micra  to  60  or  70  micra  in  diameter.     The  connective 
tissue  observed  in  the  pineal  body  of  the  ibex  is  prominent  both 
because  of  the  extensive  network  which  it  forms  and  also  on 
account  of  the  unusual  thickness  of  its  trabecular  strands.     The 
body  is  highly  vascular  and  supplied  by  a  rich  capillary  network 
(fig.  85). 

3.  Camelus  dromedarius.     In  the  camel,  as  in  Capra  hylocrius, 
four  types  of  cells  may  be  differentiated,  namely,  the  large  cells 
with   deeply  staining  nuclei,   large  cells  with  faintly  staining 
nuclei  in  which  nucleolus  and  accessory  nucleoli  are   distin- 
guishable, small  cells  with  deeply  staining,  and  small  cells  of 
faintly  staining  nuclei.     The  cellular  arrangement  has  the  same 
general  appearance  as  in  the  ibex,  although  the  tendency  toward 
the  formation  of  acini  is  not  as  pronounced.     In  the  main,  the 
arrangment  is  that  of  wide  strands  of  cells  bounded  by  irregu- 
larly disposed  trabeculae  of  connective  tissue.     The  connective 
tissue  forms  a  prominent  element  in  the  pineal  body  of  the  camel 
and  in  general  resembles  the  connective  tissue  of  the  Persian 
ibex.     The  pineal  body  in  the  camel  is  highly  vascular.     There 
were  no  concretions  observed  in  it  (fig.  86). 


180  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 


THE    PINEAL   BODY 


181 


182 


FREDERICK    TILNEY   AND    LUTHER    F.    WARREN 


THE    PINEAL   BODY  183 

4.  Zalophus   calif ornianus.     In   the   sea-lion,    although   it   is 
difficult  to  discern  the  four  types  of  cells  already  described  with 
clearness,  as  in  the  forms  already  noted,  nevertheless,  in  certain 
areas  there  appear  many  large  cells  with  extensive  nuclei  which 
stain  deeply.     Here  and  there  scattered  throughout  the  body 
appear  large  cells  of  relatively  the  same  size  as  those  just  men- 
tioned, the  nuclei  of  which,  however,  stain  but  faintly.     Small 
cells  with  deeply  staining  pycnotic  nuclei  are  present  in  numbers 
about  equal  to  that  of  the  first  type  while  a  small  variety  of 
cell  whose  nucleus  stains  feebly  is  the  least  common  variety 
observed.     The  cells  arrange  themselves  in  cords  or  columns 
which,   upon  transverse  section,   seem  to  be  circular.     These 
cords  apparently  are  much  convoluted  and  not  infrequently  a 
section  of  what  appears  to  be  the  same  cords  is  seen  in  transverse 
as  well  as  longitudinal  outline.     There  is  a  rich  connective  tissue 
network  which  appears  to  surround  the  cell  cords.     The  pineal 
body   in   Zalophus   is   highly   vascular.     No   concretions   were 
observed  (fig.  87). 

5.  Lepus  cuniculus.     In  the  rabbit  the  pineal  body  is  long  and 
cylindrical  in  form.     In  it  may  be  recognized  the  four  types  of 
cells  already  described,  the  predominant  type  being  the  large 
cell  with  abundant  granular  cytoplasm  and  a  large  deeply  stain- 
ing nucleus.     Dispersed  among  these  cells  are  small  cells  of  both 
types  and  the  large    cells    with  faintly  staining  nuclei.     The 
general  arrangement  of  the  cells  in  this  body  is  that  of  columns 
or  cords  whose  long  axes  are  transverse  to  the  axis  of  the  pineal 
gland  itself.     The  columns  of  cells  are  separated  by  delicate 
trabeculae  of  connective  tissue  in  the  meshes  of  which  capillary 
vessels  make  their  way.     Each  of  the  cell  cords  varies  in  thick- 
ness in   different  parts.     They  are  seldom  more  than  six  to 
eight  cells  deep,  but  in  some  places  their  transverse  diameter 
seems  to  be  the  thickness  of  two  cells.     The  gland  is  very  vas- 
cular and  no  concretions  are  seen  (fig.  88). 

6.  Simia  satyrus.     In  the  orang,  it  is  not  difficult  to  recognize 
the  four  types  of  cells  already  described  in  the  other  forms. 
Perhaps  the  chief  difference  in  the  histology  of  the  gland  in 
this  animal  is  the  great  prominence  which  the  large  cells  attain 


184  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 


THE    PINEAL   BODY 


185 


186  FREDERICK    TILNEY   AND    LUTHER   F.    WARREN 

both  because  of  their  tendency  to  be  collected  into  well-defined 
groups,  as  well  as  the  unusual  dimensions  of  their  cytoplasm. 
Here,  as  in  none  of  the  other  forms  already  described,  does  the 
character  of  the  pineal  cell  stand  out.  Not  only  is  it  much 
larger,  but  it  has  the  granular  appearance  so  notable  in  the 
human  pineal  cell.  The  large  cells  with  the  faintly  staining 
nuclei  are  found  scattered  among  the  cells  just  mentioned  and 
also  scattered  diffusely  throughout  the  organ.  The  small  cells 
are  less  prominent,  although  both  types  may  be  recognized. 
The  cells  are  arranged  according  to  an  apparent  design,  although 
the  large  pineal  cells  group  themselves  in  irregular  masses. 
No  tendency  to  cord  formation  is,  however,  observed.  There 
is  a  rich  and  delicate  network  of  connective  tissue,  and  many 
capillaries  surround  the  cell  masses.  No  concretions  were 
observed  (fig.  89). 

7.  Homo  sapiens.  In  the  adult  human  pineal  body  the  types 
of  cells  already  described  as  present  in  the  epiphysis  of  other 
mammals  may  be  observed  here  also.  The  large  cells  with 
granular  cytoplasm  and  large  deeply  staining  nuclei  are  the 
most  prominent  elements.  They  are  arranged  in  regular  masses 
very  similar  to  those  observed  in  Simia  saiyrus,  although  the 
intervening  areas  are  less  extensive,  so  that  in  man  the  cell 
masses  seem  to  run  into  each  other  without  sharp  line  of  demar- 
cation. A  very  dense  network  of  connective-tissue  trabeculae 
forms  the  frame  work  of  the  organ,  while  the  vascularity  of  the 
structure  is  richer  than  that  of  any  other  form  observed.  Con- 
cretions of  varying  sizes  are  present  throughout  the  entire 
gland  (fig.  90). 

The  histogenesis  of  the  pineal  gland  was  studied  in  the  cat 
and  human.  The  inception  of  differentiation  in  the  cat  presents 
itself  as  a  marked  thickening  in  the  walls  of  the  more  caudal  of 
the  two  evaginations.  In  the  70  mm.  cat  this  thickening  is  so 
pronounced  that  the  recess  in  the  anlage  is  reduced  to  a  narrow 
lumen.  The  cells  multiply  at  the  caudal  extremity  of  the  now 
almost  solid  epiphysis.  From  the  stage  of  120  mm.  to  term  a 
process  of  diverticular  formation  occurs.  This  starts  at  the 
base  of  the  gland  at  its  attachment  to  the  roof -plate  and  grad- 


THE    PINEAL  BODY 


187 


; 


188 


FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 


*A.«-?V  *«£Jk  /*  r  tf  1«P5 


THE    PINEAL   BODY  189 

ually  extends  to  its  distal  extremity.  Many  of  these  diver- 
ticula  remain  in  connection  with  the  third  ventricle,  but  as  they 
elongate  toward  the  tip  of  the  pineal  body  many  of  the  diver- 
ticula  lose  this  connection  and  finally  appear  as  blind  acini  or 
cell  cords.  In  this  way  the  original  more  or  less  indifferent  cell 
area  of  the  primitive  anlage  is  invaded  by  cells  from  the  diver- 
ticula  above  described.  Simultaneous  with  the  invasion  of 
these  diverticula,  blood  vessels  are  seen  to  make  their  way  into 
the  tissue  between  the  acini  and  cell  cords.  This  vascular 
invasion  seems  to  take  place  from  the  periphery  going  to  the 
center,  but  it  is  possible  that  independent  blood  spaces  are 
formed  which,  by  concresence,  subsequently  form  a  vascular 
network,  the  latter  coming  into  relation  with  the  blood  vessels 
surrounding  the  pineal  body.  These  characters  of  the  onto- 
genesis of  the  pineal  body  in  the  cat  are  shown  in  figure  91. 

The  process  just  described  in  the  histogenesis  of  the  cat  is 
much  better  illustrated  in  the  development  of  the  human  fetus. 
In  man,  the  process  of  diverticular  invasion  into  the  original 
cellular  mass  of  the  primitive  anlage  is  well  shown  in  figure  92, 
representing  the  condition  in  a  human  fetus  of  six  months.  Here 
it  will  be  noted  that  the  invasion  begins  at  the  base  of  the  epi- 
physis  and  manifests  itself  in  the  thick  strand  of  darkly  staining 
cells  extending  out  and  into  a  mass  of  undifferentiated  tissue. 
At  term  the  invasion  has  extended  completely  through  the  epi- 
physis  and  the  deeply  staining  strands  of  cells  are  now  arranged 
in  convoluted  cords  or  take  the  form  of  apparent  acini.  In  the 
meshes  between  these  cords  capillaries  appear  to  have  made 
their  way  in  from  the  surface  of  the  epiphysis  and  form  a  rich 
network  about  the  cell  cords  and  apparent  acini.  This  onto- 
genetic  differentiation  in  the  two  forms  just  described  would 
certainly  seem  to  indicate  a  process  which  had  as  its  object  the 
rich  vascularization  of  discretely  outlined  epithelial  areas.  Such 
a  differentiation  would  seem  to  adapt  itself  best  to  the  purposes 
of  internal  secretion. 

Marburg259  shows  in  the  development  of  the  pineal  gland  in 
man  histological  appearances  very  closely  resembling  those 
illustrated  in  figures  91,  92,  93,  and  94  of  the  authors  (fig.  95). 


190 


FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 


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i     j^yr      »_/  2 

-.,.*.,*.  - 


EH 

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THE    PINEAL    BODY 


191 


Fig.  92     Section  of  the  pineal  body  in  a  six  months  human  fetus  showing  the 
diverticular  invasion,  according  to  Tilney  and  Warren,  1917. 


192 


FBEDEBXCK    TILNEY  AND 


^ 


J 


THE    PINEAL   BODY 


193 


MEMOIR  NO.  9 


194 


FREDERICK    TILNEY   AND    LUTHER    F.    WARREN 


Marburg  also  gives  an  interesting  description  of  the  develop- 
ment of  the  suprapineal  recess  in  man  which  is  illustrated  in 
figure  96.  According  to  his  description,  the  suprapineal  recess 
is  formed  by  the  dorsal  reflection  of  the  taenia  which  originally 
was  directed  cephalad.  The  dorsal  surface  of  the  taenia  secon- 
darily becomes  fused  with  the  dorsal  surface  of  the  pineal  gland 
while  -the  ventral  surface  is  turned  dorsad.  In  this  way  the 
suprapineal  recess  results  from  a  deep  evagination  of  the  roof- 


Fig.  95  Cross  section  of  the  pineal  gland  in  a  26  mm.  human  embryo,  according 
to  Marburg,  1909. 

plate  which  comes  to  lie  above  the  pineal  body  and  extends  in 
most  cases  the  entire  length  of  that  organ.  The  suprapineal 
recess  in  its  relation  to  the  pineal  gland  in  adult  man  is  shown  in 
figure  97. 

With  reference  to  the  pineal  body  Marburg  maintains  that  in 
spite  of  all  the  involution  processes  in  the  gland,  it  cannot  be 
denied  that  even  up  to  the  late  periods  of  life  in  man  there  are 
wholly  intact  glandular  cells  present  in  the  organ  which  must 
certainly  be  taken  to  indicate  a  still  existing  function. 


^    - 


97 

Fig.  96  Scheme  showing  the  development  of  the  supra-pineal  recess,  according 
to  Marburg,  1909. 

Fig.  97     The  pineal  gland  in  man,  according  to  Marburg,  1909. 

Ch.,  commissura  habenularis;  Cp.,  commissura  posterior;  Pl.ch.,  chorioid 
plexus;  Rp.,  recessus  pinealis;  Rs,  recessus  suprapinealis;  Sch.,  pars  intercalaris; 
Th.,  taenia  habenulae;  Z,  pineal  gland. 


196  FREDERICK    TILNEY   AND    LUTHER    F.    WARREN 

7.  DISCUSSION 

1.  Significance  of  the  pineal  region 

It  is  now  possible,  with  the  facts  presented  as  evidence,  to 
discuss  the  problem  of  the  pineal  body  and,  perhaps,  to  formu- 
late some  conclusions  concerning  it. 

The  question  uppermost  about  the  epiphysis  to-day  is  whether 
the  structure  is  a  mere  vestige  or  whether  it  has,  in  mammals 
and  more  especially  in  man,  some  definite  function.  Besides 
this  highly  important  consideration  there  is  still  another  which, 
in  its  way,  has  an  even  more  far-reaching  significance,  namely, 
the  value  of  the  pineal  structures  as  one  of  the  indices  which  may 
point  out  the  lines  of  evolution  running  through  the  vertebrate 
phylum  and  those  leading  back  to  the  invertebrate,  ancestral 
stock. 

If  the  pineal  body  is  a  vestige,  it  is  essential  to  ascertain  to 
what  previously  active  structures  it  is  related  and  for  what 
reasons  it  has  become  vestigial.  In  this  sense  the  survey  of  its 
phylogenetic  relations  cannot  be  too  broad  and  should  include 
the  entire  environment  of  the  organ.  If,  as  is  held  by  many,  the 
pineal  organs  have  significance  as  a  connecting  link  between 
the  vertebrates  and  invertebrates,  then,  on  the  basis  of  embry- 
ology and  comparative  morphology,  the'  effort  must  be  made  to 
homologize  not  one,  but  all  of  the  parts  associated  with  or 
adjacent  to  the  pineal  body.  In  such  a  light  every  derivative 
of  the  roof-plate  of  the  primitive  forebrain  becomes  funda- 
mentally important,  and  no  discussion  of  the  pineal  body  could 
be  complete  which  did  not  recognize  the  character  of  the  pineal 
region  as  a  whole. 

The  portion  of  the  brain  known  as  the  pineal  region  was  first 
so  designated  by  Minot277  in  1901.  It  has  also  been  termed  the 
parietal  region.  It  extends  from  the  dorsal  extremity  of  the 
lamina  terminalis  to  the  caudal  limit  of  the  posterior  commissure 
and  comprises  a,ll  of  the  structures  which  develop  from  the  roof- 
plate  of  the  primitive  forebrain.  It  presents,  according  to 
Minot,277  a  series  of  three  arches  or  vaults,  arranged  one  in 
front  of  the  other.  The  most  cephalic  of  the  three  arches  is 


THE    PINEAL   BODY  197 

the  paraphyseal  arch,  which  extends  from  the  dorsal  extremity 
of  the  lamina  terminalis  to  the  most  cephalic  depression  in  the 
roof,  namely,  the  velum  transversum.  The  portion  of  the  roof 
immediately  caudad  of  the  velum  forms  the  middle  or  postvelar 
arch,  which  in  turn  is  separated  from  the  third  or  caudalmost 
arch  by  a  slight  depression  containing  the  superior  or  habenular 
commissure.  This  is  the  epiphyseal  arch.  In  some  species  a 
small  intercalated  portion  of  modified  gray  matter  inserts  itself 
between  the  caudal  limit  of  the  postvelar  arch  and  the  superior 
commissure.  This  is  the  pars  intercalaris  anterior.  Caudally, 
the  epiphyseal  arch  extends  toward  the  cephalic  extremity  of 
the  posterior  commissure,  but  between  the  latter  and  the  caudal 
extremity  of  the  arch  there  is  interposed  a  small  area  of  modified 
gray  matter,  the  pars  intercalaris  posterior.  The  caudalmost 
element  in  the  pineal  region  is  the  posterior  commissure,  and  to 
this,  perhaps,  should  be  added  the  subcommissural  organ,  recently 
described  by  Dendy  and  Nicolls88  and  others. 

These  structures  of  the  pineal  region  or  their  homologues  exist 
in  all  vertebrates  either  in  the  embryonic  or  adult  condition. 
The  paraphyseal  or  pre velar  arch  is  common  to  all  vertebrates. 
From  its  caudal  portion,  i.e.,  the  region  of  the  arch  nearest  the 
velum  transversum,  there  develops  a  specialized  structure,  the 
paraphysis.  This  structure,  either  in  anlage  or  as  an  adult 
organ,  appears  in  all  vertebrates. 

In  cyclostomes  (Kupffer224  in  Ammoccetes,  Burckhardt47  in 
Petromyzon)  the  paraphysis  is  a  small  sac-like  diverticulum,  if 
not  itself  highly  vascular  yet  in  close  relation  with  the  vascular 
mesenchyme  immediately  above  it.  In  selachians  (Minot277 
and  Locy243  in  Acanthias)  the  structure  is  a  small  outgrowth 
from  the  paraphyseal  arch.  In  ganoids  (Kupffer223  in  Acipenser, 
Hill,180  Eycleshymer  and  Davis113  in  Amid)  the  paraphysis  is  a 
large  diverticulated  and  vascular  organ.  In  many  teleosts 
(Burckhardt,47  Studnicka,391  and  Terry)392  the  paraphysis  appears 
to  be  rudimentary.  In  dipnoians  (Burckhardt44  in  Protopterus) 
the  organ  is  a  wide  outgrowth  with  many  small  diverticula  and 
rich  in  blood  vessels.  The  paraphysis  in  amphibians  attains  its 
greatest  conspicuity  as  an  organ.  It  is  highly  differentiated  in 


198  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

the  adult  (Warren416  in  Necturus,  Osborn289  in  Siredon,  Siren 
and  Proteus.)  It  is  an  elaborately  folded,  glandular  structure 
(Burckhardt43  in  Triton  and  Ichthyophis) ,  a  solid  vascular 
mass  (Sorensen361  in  Menopoma),  or  a  tubular  and  digitated 
structure  (Eycleshymer112  in  Amblystoma).  In  Rana,  accord- 
ing to  Minot,277  the  paraphysis  is  characterized  by  a  glandular 
epithelium,  a  tubular  arrangement  of  its  cells,  and  an  appar- 
ently sinusoidal  circulation,  In  Lacertilia  (Warren415  in  Lacerta 
muralis,  L.  agilis  and  L.  viridis)  it  is  large  and  glandular  in 
character,  forming  a  conspicuous  element  of  the  pineal  region. 
In  many  instances  it  is  so  extensive  as  to  reach  caudad  as  far 
as  the  midbrain,  or  even  the  cerebellum.  In  ophidians,  chelo- 
nians  and  crocodilians,  the  paraphysis  is  small  and  rudimentary. 
In  birds  it  was  first  demonstrated  in  the  chick  by  Selenka352  and 
later  described  by  Minot277  in  the  chick  and  Burckhardt46  in 
the  embryo  crow.  Dexter90  found  it  constant  in  the  chick  and 
common  fowl.  He  believes  it  to  be  a  gland  in  which  there  are 
no  sensory  elements. 

In  mammals  Selenka352  gave  the  first  description  of  the  para- 
physis in  the  opossum.  Francotte128  observed  it  in  a  12  mm. 
human  embryo.  Usually,  however,  although  it  has  been  recog- 
nized in  anlage,  in  mammals  it  disappears  early  and  the  para- 
physeal  arch  bears  no  trace  of  it  in  the 'fetal  period. 

Thus  it  will  be  seen  that  the  glandular  nature  of  the  para- 
physis in  the  middle  portion  of  the  phyletic  series,  including 
amphibia  and  lacertilia,  is  quite  beyond  dispute.  Some  of  this 
character  it  retains  in  the  more  modern  reptiles  and  birds.  On 
the  other  hand,  it  is  relatively  inconspicuous  as  an  organ  among 
the  lowest  vertebrates  and  disappears  altogether  is  most  mam- 
mals. Manifestly,  therefore,  whatever  tendency  toward  speciali- 
zation the  paraphysis  presents  is  in  the  interest  of  glandular 
formation.  As  a  gland,  it  appears  either  to  contribute  its  secre- 
tion directly  to  the  cerebrospinal  fluid  in  the  ventricles  or  in- 
directly to  the  blood.  In  no  instance  is  there  evidence  of  a 
tendency  toward  the  development  of  sensory  structure  nor  do 
the  histological  elements  entering  into  the  paraphysis  suggest 
its  direct  participation  in  any  neural  mechanism. 


THE    PINEAL   BODY  199 

From  the  remainder  of  the  paraphyseal  arch  there  develop 
in  many  classes  of  vertebrates  several  chorioidal  processes.  In 
cyclostomes,  selachians,  teleosts,  and  ganoids,  two  such  plexuses, 
more  or  less  well  developed,  may  be  recognized,  namely,  the 
lateral  and  inferior  telencephalic  chorioid  plexuses.  The  inferior 
chorioid  plexus  attains  its  most  marked  proportions  in  amphibia, 
while  in  all  of  the  higher  vertebrates  its  prominence  declines. 
This  is  likewise  true  of  the  lateral  chorioid  plexus.  Histologi- 
cally  and  topographically,  the  significance  of  these  plexuses  is 
not  difficult  to  discern;  their  rich  vascularization,  their  tendency 
toward  glomerular  arrangement  together  with  the  relations  and 
modifications  of  the  ependymal  cells  which  enter  into  them 
leave  little  room  to  doubt  that  they  are  glandular  in  nature. 
Indeed,  the  present  tendency  is  to  refer  to  these  structures  as 
chorioidal  glands,  thus  deputing  to  them  a  definite,  secretory 
function  in  relation  to  the  cerebrospinal  fluid.  Even  the  older 
conceptions  of  the  chorioid  plexuses  recognized  this  physio- 
logical possibility  in  connection  with  the  plexuses. 

The  morphological  fact  concerning  the  first  and  most  cephalic 
of  the  three  arches  in  the  pineal  region  discloses  a  predominant 
tendency  for  its  derivatives  to  give  rise  to  glandular  structures, 
while,  on  the  other  hand,  there  is  no  evidence  that  it  has  ever 
been  engaged  in  definite  neural  mechanisms. 

The  structure  which  forms  the  boundary  between  the  prevelar 
or  paraphyseal  arch  and  the  postvelar  arch  is  the  velum  trans- 
versum.  Like  the  paraphyseal  arch,  it  attains  its  greatest  con- 
spicuity  in  the  lower  vertebrates  and  in  the  higher  forms  becomes 
less  prominent.  In  mammals  its  appearance  is  most  pronounced 
in  the  embryonic  period  from  which  time  it  becomes  progres- 
sively reduced,  being  present  in  the  adults  of  most  orders  as  a 
more  or  less  well-marked  rudiment.  In  most  classes  of  verte- 
brates it  becomes  associated  with  a  dense  mesenchymatous  in- 
vasion which  results  in  a  fairly  rich  vascularization.  This  com- 
bination of  ependymal  cells  and  blood  vessels  often  takes  the  form 
of  a  plexus,  and  when  such  is  the  case  the  velum  transversum 
aligns  itself  with  the  structures  derived  from  the  paraphyseal 
arch  in  the  absence  of  any  definitely  neural  elements  and  ths 
tendency  toward  glandular  formation. 


200  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

The  middle  or  post  velar  arch  (so  called  by  Minot277)  in  the 
pineal  region  has  also  been  designated  the  Zirbelpolster  by 
Burckhardt,47  the  postparaphysis  by  Sorensen,361  the  dorsal  sac 
by  Goronowitsch,153  and  the  roof  of  the  parencephalon  by 
Kupffer.226  This  structure,  with  few  exceptions,  forms  a  prom- 
inent element  of  the  pineal  region  throughout  the  vertebrate 
series.  In  cyclostomes  it  is  present  as  a  simple  membranous 
sac  with  scant  vascularity  of  its  own,  although  in  close  approxi- 
mation with  the  highly  vascular  mesenchyme  dorsal  to  it.  In 
selachians  it  is  usually  somewhat  more  extensive  yet  similar  in 
its  structural  details.  In  ganoids  it  becomes  immensely  ex- 
panded as  shown  by  Balfour,11  Huxley,191  Wiedersheim,425 
Goronowitsch,153  Wilder,428  and  Kingsbury.204  Herrick178  describes 
the  dorsal  sac  as  a  pouch  lined  with  a  single  row  of  ependymal 
cells  with  long  cilia  which  appear  to  be  of  the  epithelial,  secre- 
tory type.  It  is  highly  vascular  in  these  fish.  In  teleosts,  on 
the  other  hand,  it  is  not  always  prominent,  In  Opsanus,  Terry392 
found  that  the  dorsal  sac  was  small  and  perhaps  disappeared 
altogether.  In  some  teleosts,  as  in  ganoids,  the  postvelar  arch 
is  not  only  highly  vascular,  but  presents  ridges,  secondary  folds, 
and  diverticula.  In  amphibia,  reptiles,  and  birds,  the  postvelar 
arch  becomes  definitely  associated  with  the  formation  of  the 
chorioid  plexuses,  and  it  does,  in  fact,  contribute  the  epipthelial 
elements  to  the  chorioid  plexus  of  the  diencephalon.  With  the 
advent  of  the  corpus  callosum  in  mammals  the  dorsal  sac  or 
postvelar  arch  becomes  somewhat  overshadowed,  due  to  the 
introduction  of  the  transverse  commissure  which  lies  above  and 
tends  to  flatten  it.  It,  however,  loses  none  of  its  tendency  to 
participate  in  the  plexus  formation,  which  latter  in  mammals 
-attains  a  greater  development  than  in  many  of  the  lower  forms. 

This  element  of  the  pineal  region,  therefore,  is  to  be  associated 
with  the  paraphyseal  arch  in  its  tendency  toward  specialization 
From  the  lowest  vertebrates  upward  through  the  phylum  it 
manifests  no  attempt  toward  the  development  of  sensory  or 
other  definitely  neural  elements,  while  the  entire  trend  of  its 
evolution  reveals  a  glandiferous  potentiality. 


THE    PINEAL    BODY  201 

The  postvelar  arch  is  separated  from  the  caudalmost  or  epi- 
physeal  arch  of  the  pineal  region  by  a  shallow  invagination  of 
the  diencephalic  roof,  which  usually  contains  commissural 
nerve  fibers.  This  is  known  as  the  superior  commissure  or 
commissura  habenularis.  In  some  forms,  as  in  amphibia,  it  is 
associated  with  a  small,  somewhat  thickened  area  of  the  roof  in 
which  the  histological  elements  are  largely  neuroglia.  This  is 
the  pars  intercalaris  anterior.  Although  the  structure,  or  its 
homologue,  occurs  in  such  a  limited  number  of  animals,  its 
recognition  as  a  distinct  part  seems  advisable  in  the  description 
of  this  area  of  the  brain.  In  cyclostomes,  prosaurians,  and 
saurians,  the  superior  or  habenular  commissure  seems  to  be 
connected  with  the  parapineal  or  parietal  nerve  and,  perhaps, 
through  this  relation  is  brought  into  connection  with  the  end- 
vesicle  of  the  parapineal  organ.  If  such  is  the  case,  it  may  well 
be  that  this  commissure  in  cyclostomes,  in  prosaurians,  and  in 
saurians  is  related  to  an  organ  of  special  sense.  In  this  light 
the  superior  commissure  must  be  accounted  as  engaged  in  the 
organization  of  a  specialized  neural  mechanism,  and  thus  be- 
comes the  first  of  the  structures  encountered  in  the  pineal  region 
to  show  this  tendency  in  differentiation.  The  significance  of  the 
pars  intercalaris  anterior  is  not  altogether  clear,  although  it  is 
possible  that  it  may  represent  a  residue  of  an  unutilized  susten- 
tacular  area  developed  in  the  interest  of  the  commissural  forma- 
tion. The  presence  in  it  of  a  few  nerve  fibers  would  seem  to 
substantiate  this  view. 

The  caudalmost  or  epiphyseal  arch  is  by  far  the  most  complex 
of  the  three  arches  in  the  pineal  region.  In  order  that  its  de- 
scription may  be  comprehensive  enough  to  include  all  verte- 
brates, a  number  of  different  elements  are  to  be  recognized, 
either  as  appearing  in  the  embryo  or  giving  rise  to  definite  adult 
structures  whose  composit  may,  for  convenience,  be  termed  the 
epiphyseal  complex.  This  complex,  then,  consists  of  two  princi- 
pal organs,  namely,  the  pineal  organ  and  the  parapineal  organ. 
Each  of  these  organs  is  in  turn  susceptible  of  subdivision  into 
certain  portions  as  follows: 


202  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

1.  Pineal  organ.  2.  Parapineal  organ. 

a)  Proximal  portion.  a)  Proximal  portion. 

6)  Stalk.  b)  Stalk. 

c)  End-vesicle.  c)  End-vesicle. 

Of  all  of  these  parts  the  proximal  portion  of  the  pineal  organ 
is  phyletically  the  most  constant,  occurring  in  all  classes  of 
vertebrates.  The  stalk  and  end- vesicle  of  the  pineal  organ 
are  much  less  constant,  for  they  cease  to  appear  in  ophidians 
and  are  absent  in  all  the  forms  higher  than  the  snakes.  The 
parapineal  organ  as  a  whole  is  limited  to  but  a  few  classes  of 
vertebrates.  It  is  prominent  only  in  cyclostomes,  in  prosaurians 
and  saurians.  It  is  rudimentary  in  ganoids  and  teleosts.  It  is 
developmentally  transitory  or  entirely  absent  in  selachians, 
amphibia,  ophidians,  chelonia,  crocodilians,  birds,  and  mammals. 

Considered,  for  a  moment,  quite  apart  from  the  inferences 
which  may  be  drawn  from  the  intrinsic  structural  characters  of 
the  epiphyseal  complex  itself,  there  is  one  outstanding  feature 
of  unquestionable  importance,  namely,  the  genetic  association  of 
this  complex  with  a  series  of  organs  which  under  no  conditions 
have  manifested  a  tendency  to  become  specialized  in  the  interest 
of  definitive  neural  mechanisms,  but  which,  wherever  differ- 
entiated, have  given  rise  to  glandular  tissue. 

The  caudalmost  element  in  the  pineal  region  is  the  posterior 
commissure.  It  is,  perhaps,  not  definitely  settled  that  this 
assignment  of  the  commissure  to  the  interbrain  is  in  all  respects 
justifiable.  If,  however,  it  is  to  be  accounted  as  a  structure  of 
the  pineal  region,  the  function  of  the  commissure  appears  to  be 
related  to  a  specialized  portion  of  the  pineal  organ,  namely,  the 
end- vesicle,  with  which  latter  the  posterior  commissure  is  said  to 
be  in  connection  by  means  of  nerve  fibers.  Admitting,  for  the 
moment,  the  correctness  of  the  morphological  and  physiological 
interpretation  given  the  subcommissural  body  by  Dendy  and 
Nicolls,88  the  structure  may  tentatively  be  considered  as  a 
part  of  the  pineal  region.  Its  function,  apparently,  is  in  some 
way  connected  with  the  fiber  of  Reissner  and  the  entire  organ 
thus  associated  with  equilibration.  Both  of  these  elements, 


THE    PINEAL    BODY  203 

constituting  the  •  caudalmost  constituents  of  the  pineal  region, 
are  obviously  specialized  as  neural  mechanisms  in  the  interest  of 
special  sense  receptors.  The  pars  intercalaris  posterior  has,  no 
doubt,  the  same  functional  significance  as  the  anterior  inter- 
calated area  associated  with  the  superior  commissure. 

From  a  review  of  the  several  structures  associated  with  the 
epiphyseal  complex  in  the  pineal  region,  it  is  clear  that  the 
majority  of  them  when  differentiated  at  all  give  rise  to  glandular 
organs,  while  those  which  participate  in  neural  mechanisms  are 
not  only  in  the  minority,  but  constitute  a  relatively  small  portion 
of  this  area  in  the  brain.  Thus  the  paraphysis  and  paraphyseal 
arch  as  a  whole,  the  velum  transversum,  and  the  post  velar  arch 
are  genetically  glandiferous,  while  the  superior  commissure  and 
posterior  commissure  alone  bear  any  apparent  relation  to  neural 
activity. 

In  view  of  these  facts,  it  would  seem  that  whatever  the  func- 
tions of  the  epiphyseal  complex  may  be,  the  morphogenetic 
impulse  imparted  to  it  from  a  region  of  the  brain  so  preponder- 
atingly  glandiferious  in  its  constituents  could  not  fail  to  have 
a  profound  influence  upon  the  evolutional  adaptation  of  the 
epiphysis.  Yet,  in  spite  of  the  illumination  which  this  genetic 
association  of  the  epiphyseal  complex  with  definitely  glandular 
structures  seems  to  shed  upon  its  inherent  tendencies  in  differ- 
entiation, it  must  be  in  the  intrinsic  characters  of  the  complex 
itself  that  the  solution  of  its  problem  is  ultimately  to  be  sought. 

2.     Evidence    based   on   the   gross   morphology   of  the  epiphyseal 

complex 

a.  Phyletic  constancy.  If  such  evidence  as  may  be  obtained 
from  the  gross  morphology  of  the  epiphyseal  complex  is  taken 
into  account,  a  number  of  reasons  may  be  advanced  to  show 
that  it  is  quite  impossible  to  conceive  of  the  pineal  body  as  a 
vestigial  structure.  These  reasons  seem  so  cogent  as  to  place 
upon  the  arguments  which  would  refute  them  an  unusually 
heavy  burden. 


204  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

The  most  significant  feature  with  reference  to  the  functional 
activity  of  the  pineal  body  appears  to  be  the  fact  of  its  marked 
phyletic  constancy.  Certainly,  a  structure  which  is  marked  for 
regression  or  in  which  it  is  claimed  that  the  evidences  of  regres- 
sion may  easily  be  found,  would  scarcely  show  such  remarkable 
tenacity  throughout  the  phylum.  Its  occurrence  in  cyclostomes, 
in  all  the  fish,  in  amphibians  and  reptiles,  in  birds  and  mammals 
reveals  it  as  a  structure  which  must  have  been  called  into  being 
in  response  to  some  definite  demand,  for  why,  otherwise,  should 
all  of  these  classes  of  vertebrates  so  constantly  present  this 
morphologic  condition? 

It  is,  perhaps,  laying  overmuch  stress  upon  the  phyletic 
constancy  of  the  epiphyseal  complex  to  draw  from  these  facts 
alone  the  inference  that  it  must  be  a  physiologically  active 
organ.  Its  reported  absence  in  the  Myxinoids,  in  Torpedo 
ocellata,  and  Torpedo  marmorata  as  well  as  in  Crocodilia  would 
seem  to  call  into  question  the  full  value  attached  to  the  argu- 
ment of  its  otherwise  general  constancy.  On  the  other  hand,  it 
must  not  be  overlooked  that  in  the  history  of  the  observations 
devoted  to  the  pineal  body,  a  relatively  large  number  of  investi- 
gators have  reported  the  absence  of  the  epiphysis  in  one  form 
or  another,  only  to  have  their  error  corrected  by  subsequent 
research  and  the  presence  of  the  organ  •  clearly  demonstrated. 
By  far  the  greater  majority  of  observers  in  the  morphology  of 
this  portion  of  the  brain  are  to-day  of  the  opinion  that  the 
epiphyseal  complex  as  a  whole  or  in  some  of  its  parts  exists  in 
all  vertebrates.  It  is  certainly  pertinent  to  the  reported  absence 
of  the  organ  in  the  forms  mentioned  to  recall  Kidd's203  observa- 
tion that  the  conditions  in  Torpedo  need  further  review  before 
final  acceptance  of  the  statement  that  the  epiphysis  is  absent  in 
these  forms.  The  same  also  applies  to  Crocodilia,  and  until 
this  order  has  been  more  extensively  examined,  much  reserva- 
tion should  be  made  in  concluding  that  the  pineal  body  is  absent 
in  these  reptiles.  Again,  Kidd's203  contention  with  reference  to 
the  Myxinoids  adds  another  view  which  would  render  less  serious 
the  reported  absence  of  the  epiphysis  in  the  forms  mentioned. 
According  to  Kidd,  it  is  not  surprising  that  in  Myxinoids  the 


THE    PINEAL   BODY  205 

epiphysis  is  wanting,  since  these  are  considered,  by  most  author- 
ities, as  degenerated  forms. 

With  these  exceptions,  then,  so  much  in  the  minority,  this 
negative  evidence  should  be  accepted  with  much  hesitancy. 
In  fact,  the  phyletic  constancy  of  the  epiphyseal  complex  is  so 
pronounced  as  to  render  the  total  absence  of  the  organ  in  Myxi- 
noids,  Torpedo,  and  Crocodilia  open  to  doubt. 

b.  Phyletic  variations  and  morphologic  specialization.  If  the 
constancy  already  considered  lends  itself  to  the  weight  of  evi- 
dence in  favor  of  the  supposition  that  the  pineal  body  is  a  func- 
tional organ,  then  even  more  will  the  phyletic  variations  and 
morphologic  specializations  which  present  themselves  in  this 
organ  support  the  view  that  the  epiphysis  is  not  a  vestige,  but 
plays  some  physiologically  definite  role. 

Certainly,  when  the  marked  specialization  in  the  epiphyseal 
complex  in  the  various  orders  of  vertebrates  is  taken  into  ac- 
count, it  is  difficult  to  escape  the  conclusion  that  such  modifica- 
tions must  have  been  in  the  interest  of  definite  adaptations. 
If  these  specializations  referred  to  were  indefinite  or  diffuse,  it 
might  still  be  a  question  whether  the  processes  were  actually  in 
the  interest  of  adaptation;  but  when,  as  is  the  case,  form  after 
form  shows  such  a  high  state  of  differentiation,  such  a  definite  and 
discrete  specialization,  there  seems  to  be  little  room  for  doubt 
that  a  process  of  adaptation  has  been  carried  forward  in  order 
to  satisfy  the  demands  for  the  development  of  specialized  organs. 

On  the  other  hand,  it  cannot  be  denied  that  even  such  discrete 
differentiation  as  the  epiphyseal  complex  presents  in  many 
forms,  may  represent  but  the  rudiments  of  an  adaptive  process 
which  in  some  extinct  forms,  or  perhaps  even  in  some  of  the 
proto- vertebrates,  may  have  attained  their  functional  consum- 
mation only  to  impart  an  impulse  in  this  direction  to  those  verte- 
brates which  show  the  most  definite  specialization  in  the  pineal 
organs. 

In  this  sense,  all  of  the  differentiation  of  the  epiphyseal  com- 
plex throughout  the  vertebral  phylum  expresses  an  inherent 
attempt  to  consummate  the  formation  of  organs  which  have 
been  essential  in  extinct  forms  or  in  the  ancestors  of  the  verte- 


206  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

brates.  This  contention,  while  it  must  have  its  place  in  the 
discussion,  seems  to  lose  force  in  view  of  the  special  development 
of  the  pineal  organ  in  certain  vertebrates.  Thus,  in  cyclostomes 
there  is  present,  to  a  degree  seen  in  no  other  vertebrates,  a 
development  of  the  major  constituents  of  the  epiphyseal  com- 
plex. That  is  to  say,  both  the  pineal  organ  and  parapineal 
organ  attain  a  degree  of  differentiation  which  at  least  justifies 
the  supposition  that  one,  if  not  both  of  them  have  functional 
activities  of  a  visual  nature.  The  presence  in  these  forms  of  a 
well-marked  retinal  structure,  seen  in  the  pineal  organ  as  well 
as  in  the  parapineal  organ,  an  end-vesicle  containing  a  syncytial 
structure  comparable  in  many  respects  to  the  vitreous,  a  pig- 
ment-free, ectal  wall  enclosing  the  end-vesicle  and  resembling  a 
lens,  together  with  a  bundle  of  nerve  fibers  connected  with  the 
posterior  commissure  in  the  case  of  the  pineal  organ,  and  the 
superior  commissure  in  the  case  of  the  parapineal  organ,  con- 
stitute irrefutable  evidence  of  morphological  specialization 
adapting  the  organ  to  photo-receptive,  if  not  visual  purposes. 
This  supposition  is  further  borne  out  by  the  fact  that  the  organs 
in  their  development  grow  rapidly  away  from  the  roof  of  the 
brain  and  ultimately  take  up  a  position  which,  from  its  relation 
to  the  surface  of  the  body,  affords  certain  epiphyseal  structures 
the  best  opportunity  of  becoming  distance  receptors.  From  the 
striking  position  which  the  pineal  and  parapineal  organs  hold  in 
the  vault  of  the  skull,  lodged  as  they  are  in  a  deep  fossa,  it  would 
seem  evident  that  they  have  become  so  situated  that  they  might 
the  more  readily  receive  sensory  impulses  impinging  upon  the 
surface  of  the  head. 

That  this  visual  or  photo-receptive  tendency  in  the  selachians, 
ganoids,  and  teleosts  should  almost  altogether  disappear,  al- 
though the  pineal  organ  itself  remains  as  a  conspicuous  struc- 
ture, would  speak  in  favor  of  a  pluripotentiality  in  the  differen- 
tiation of  the  epiphyseal  complex.  It  is  certain  that  in  the 
higher  fish  there  is  no  evidence  pointing  to  the  development  of 
anything  resembling  the  visual  structures  observed  in  cyclo- 
stomes. In  selachians  the  parapineal  organ  is  entirely  absent; 
the  pineal  organ,  on  the  other  hand,  is  a  large  and  prominent 


THE    PINEAL   BODY  207 

structure  presenting  a  proximal  portion,  a  prolonged  stalk,  and 
a  fairly  well  marked  end-vesicle.  No  tendency,  however,  is 
observed  toward  the  development  of  a  photo-receptive  appara- 
tus. The  thickened  proximal  portion  communicates  directly 
with  the  ventricle  on  the  one  hand,  and  through  the  stalk  with 
the  end- vesicle  on  the  other.  The  fact  that  this  latter  portion 
of  the  pineal  organ  is  lodged  in  a  deep  fossa  of  the  skull  and  thus 
brought  into  close  relation  with  the  epidermis,  would  favor  the 
belief  that  in  this  structure  may  be  observed  the  arrested  or 
abortive  effort  toward  the  formation  of  a  physiological  organ. 
That  this  organ,  however,  deprived  of  the  opportunity  to  reach 
such  a  goal  in  its  differentiation,  should  remain  so  prominent  a 
structure  connected  with  the  brain,  would  seem  to  refute  the 
conception  that  it  is  a  mere  vestige  or  rudiment;  indeed,  it 
seems  to  compel  the  belief  that  it  exists  in  the  interest  of  some 
other  function  as  yet  not  entirely  clear. 

When,  however,  the  finer  histological  structure  of  the  pineal 
organ  in  selachians  is  discussed,  it  may  be  possible  to  disclose 
evidence  which  will  at  least  suggest,  that  the  structure  in  these 
forms  is  functionally  active.  The  point  which  the  gross  mor- 
phological conditions  in  selachians  does  lay  emphasis  upon  is  the 
presence  of  so  prominent  a  structure,  showing  no  evidence  in 
itself  of  retrogression  and  yet  quite  devoid  of  such  specializa- 
tion as  would  connect  it  definitely  with  visual  function. 

In  the  teleosts,  the  observation  made  with  reference  to  the 
selachians  assumes  even  more  importance,  for  here  the  pineal 
organ  shows  a  marked  specialization  which  is  entirely  contrary 
to  the  lines  of  differentiation  followed  in  the  development  of  a 
visual  organ.  In  most  of  the  teleosts  the  pineal  organ  presents 
a  small  proximal  portion,  a  relatively  short  stalk,  and  a  volumi- 
nous thick-walled  end-vesicle.  The  general  follicular  appear- 
ance of  the  end-vesicle,  together  with  its  relatively  large  size 
and  the  fact  that  it  has  neither  migrated  to  such  a  great  distance 
from  the  roof-plate  of  the  interbrain  nor  come  to  occupy  a  defi- 
nite fossa  in  the  vault  of  the  skull,  all  go  to  disprove  any  inherent 
tendency  in  the  structure  to  differentiate  as  a  visual  organ.  In 
many  teleosts  a  small  parapineal  organ  develops,  but  never 


208  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

reaches  dimensions  comparable  with  the  pineal  organ.  As  in 
the  case  of  the  selachians,  the  histology  of  the  pineal  organ  of 
the  teleost  will  prove  helpful  in  the  interpretation  of  its  function. 

Thus,  in  the  four  great  classes  of  fish,  cyclostomes,  selachians, 
ganoids,  and  teleosts,  the  epiphyseal  complex  shows  a  remark- 
able variation  in  its  specialization,  and  while  the  tendency  to 
develop  visual  or  photo-receptive  structures  is  marked  in  the 
cyclostomes,  it  is  suspended,  if  not  entirely  absent,  in  selachians, 
ganoids,  and  teleosts. 

In  the  latter  forms,  however,  the  epiphyseal  complex  is  so 
conspicuous  an  element  of  the  brain  as  to  make  the  conclusion 
that  it  is  without  function  a  difficult  one  to  maintain.  For  these 
reasons,  it  would  seem  justifiable  to  conclude  that  the  epiphyseal 
complex  is  pluripotential  in  its  specialization  and  that  while  it 
may  be  vested  with  the  possibility  of  giving  rise  to  a  visual  or 
photo-receptive  apparatus,  it  may  and  does  become  differ- 
entiated as  organs  having  some  significance  other  than  sensory. 

Still  greater  modifications  present  themselves  in  the  amphibia, 
for  in  these  forms  the  pineal  organ  shows  an  even  more  marked 
differentiation  than  any  of  the  other  lower  classes.  The  para- 
pineal  organ  does  not  develop  in  urodela  or  anura.  When,  how- 
ever, the  structure  of  the  pineal  organ  is  considered,  the  fact 
that  it  develops  a  proximal  portion  of  such  conspicuous  dimen- 
sions as  to  be  secondary  to  the  paraphysis  in  the  roof  of  the 
interbrain,  from  the  free  extremity  of  which  there  extends  a  thin 
nerve  filament  connecting  with  an  end-vesicle,  it  becomes  clear 
that  the  entire  process  of  adaptation  in  this  instance  cannot  be 
in  the  interest  of  sensory  function,  for  if  that  were  the  case, 
why,  then,  should  the  proximal  portion  of  the  pineal  organ 
assume  such  conspicuity? 

Stieda's379  interpretation  of  the  end- vesicle  in  amphibia  as  a 
frontal  subcutaneous  gland  is,  of  course,  quite  untenable,  since 
the  end-vesicle  manifests  by  its  position  and  connections  some 
obvious  adaptation  to  sensory  activity.  Yet  to  its  proximal 
portion  might  well  be  attributed  a  glandular  function,  not 
only  because  of  its  unusually  large  dimensions,  but  also  because 
of  the  position  which  it  holds  with  reference  to  the  third  ventricle. 


THE    PINEAL   BODY  209 

If  the  argument  bearing  upon  the  pluripotentiality  of  specializa- 
tion of  the  epiphyseal  complex  needed  support  or  confirmation, 
this  is  found  in  the  conditions  of  amphibians. 

The  evidence  afforded  by  the  reptiles  goes,  perhaps,  as  far 
as  may  be  deemed  necessary  to  confirm  the  pluripotentiality  of 
the  pineal  organ  and  its  derivatives.  In  the  ancient  and  primi- 
tive reptiles,  including  the  prosaurians  and  saurians,  there  is  a 
tendency  for  both  pineal  and  parapineal  organs  to  attain  remark- 
able development.  But  in  these  forms,  it  is  the  parapineal  organ 
which  assumes  predominance  in'  the  development  of  a  sensory 
apparatus.  In  sphenodon  and  many  of  the  lizards  the  parietal 
or  third  eye  reaches  such  a  high  state  of  differentiation  as  to 
leave  little  doubt  concerning  its  visual  function.  The  well 
marked  optic  vesicle,  lodged  in  a  parietal  fossa  and  brought  into 
relation  with  the  external  epidermis  by  means  of  specialized  cells, 
affords  incontrovertible  evidence  that  this  organ  is  adapted  as  a 
distance  receptor.  The  pineal  organ,  while  it  presents  some 
tendency  towards  the  development  of  a  visual  organ,  does,  as  a 
matter  of  fact,  fall  far  short  of  such  attainment.  Its  end- vesicle 
is  smaller  than  in  any  of  the  other  forms  already  considered. 
Its  stalk  is  shorter;  on  the  other  hand,  its  proximal  portion  has 
assumed  characters  not  as  yet  observed  in  the  lower  members  of 
the  vertebrate  series.  So  pronounced  is  the  specialization  of 
this  proximal  portion  that  it  needs  no  microscopic  investigation 
to  disclose  the  marked  differentiation  of  the  structure.  Its 
walls  are  not  only  thick  and  convoluted,  giving  it  a  lobulated 
appearance,  but  its  diameters  are  greater  than  those  of  the 
lower  forms. 

Upon  passing  to  the  more  modern  reptiles,  including  the 
ophidians  and  chelonians,  the  tendency  to  specialization  which 
has  previously  been  emphasized  in  this  discussion,  receives  still 
further  accentuation.  In  these  forms,  the  parapineal  organ  dis- 
appears altogether  and  nothing  remains  to  indicate  that  it  ever 
had  existence  in  reptilia.  There  is  no  parietal  fossa  and  no 
specialization  of  the  cutaneous  surface  in  the  head  which  might 
even  vaguely  suggest  the  remnants  of  the  parietal  eye  so  con- 
spicuous in  the  ancient  reptiles.  Yet,  on  the  other  hand,  the 

MEMOIR  NO.  9 


210  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

pineal  organ  manifests  such  marked  alterations  as  to  leave  no 
doubt  that  a  process  of  specialization  is  going  on  in  this  struc- 
ture. It  is  a  much  more  voluminous  organ  having  a  greater 
solidity  and  presenting  only  one  of  the  three  fundamental  por- 
tions observed  in  the  pineal  organ  of  the  lower  forms.  The 
end- vesicle  and  the  stalk  of  the  end-vesicle  have  disappeared. 
The  proximal  portion  alone  remains  to  represent  the  epiphyseal 
complex.  It  also  manifests  certain  modifications  in  its  relation 
to  the  brain,  since  now  it  no  longer  communicates  with  the  ven- 
tricle through  a  canal.  Furthermore,  it  has  developed  a  shallow 
intermediate  stem  or  stalk  connecting  it  with  the  roof-plate. 

The  inception  of  the  process  resulting  in  the  formation  of 
the  pineal  peduncle  is  first  witnessed  in  the  sphenodon  and 
lacertilia.  The  conditions  in  birds  and  mammals  show  a  still 
further  tendency  along  the  lines  of  specialization  first  manifested 
in  ophidians,  for,  as  in  these  latter  forms,  neither  the  parapineal 
organ  nor  the  end-vesicle  or  stalk  of  the  pineal  organ  makes  its 
appearance.  The  epiphysis  in  many  of  the  birds  becomes  a 
solid  organ  with  no  canal  connecting  it  with  the  third  ventricle, 
although  in  certain  birds  this  canal  is  present.  In  mammals  the 
canal  has  never  been  observed  and  the  pineal  body  presents 
itself  as  a  dense,  solid  structure  in  close  proximity  to  the  roof  of 
the  interbrain  or  resting  upon  the  roof-plate  of  the  midbrain. 

Another  observation  made  by  Kidd203  is  pertinent  in  this  con- 
nection, to  the  effect  that  if  nature  is  endeavoring  to  be  rid  of 
the  pineal  body  it  has  taken  a  remarkably  long  time  imper- 
fectly, if  at  all,  to  accomplish  this  end.  The  evidence  that  the 
reptiles  in  the  Palaeozoic  era  possessed  a  parietal  eye  is  sub- 
stantiated by  the  parietal  foramen  in  these  extinct  forms,  as 
demonstrated  by  Bashford  Dean.82 

All  of  this  evidence  concerning  the  phyletic  variations  and 
morphologic  specialization  seems  to  justify  the  conclusion  that 
the  epiphyseal  complex  is  possessed  of  a  pluripotentiality  which 
in  a  few  forms  has  been  realized  as  a  more  or  less  diffuse  visual 
structure,  but  which  fundamentally  appears  to  be  in  the  interest 
of  a  differentiation  whose  functionl  significance  is  not  sensory. 


THE    PINEAL   BODY  211 

c.  Relative  constancy  of  the  epiphyseal  complex  with  reference 
to  other  structures  of  the  pineal  region.     The  phyletic  constancy 
of  the  epiphyseal  complex,  when  considered  in  conjunction  with 
the  other  derivatives  of  the  diencephalic  roof-plate,  brings  to 
light  a  fact  of  no  little  significance.     It  has  already  been  shown 
how  constant  the  epiphyseal  complex,  either  in  its  entirety  or 
in  some  of  its  parts,  is  in  the  vertebrate  phylum,  and  this  be- 
comes further  emphasized  by  the  fact  that,  this  structure  alone 
of  all  the  elements  derived  from  the  roof-plate  presents  such 
undeniable  constancy.     If  compared  with  one  of  the  most  con- 
spicuous roof-plate  derivatives,  the  paraphysis,  the  epiphyseal 
complex  stands   out  in  marked   contrast.     The  paraphysis  is 
present  in  its  highest  state  of  evolution  in  the  middle  of  the 
vertebrate  series;  that  is  to  say,  in  amphibians  and  in  older 
reptiles.     It  is  a  conspicuous  organ,  showing  but  little  differ- 
entiation in  cyclostomes  and  in  fishes  generally.     In  ophidians, 
birds,  and  mammals  it  is  absent.     The  inference  which  may  be 
drawn  from  these  facts  seems  to  be  that  the  roof-plate  of  the 
interbrain  is  capable  of  developing  a  structure  which,  when  it  no 
longer  subserves  any  purpose,  ceases  to  exist.     When  the  phy- 
letic constancy  of  the  epiphyseal  complex  is  compared  with  that 
of  the  paraphysis,  it  would  seem  evident  that  this  very  constancy 
argues  a  demand  on  the  part  of  the  organ  for  the  presence  in  the 
animal  of  this  complex  or  some  of  its  parts. 

To  a  less  degree,  the  comparison  in  favor  of  the  pineal  organs 
may  be  drawn  with  reference  to  the  velum  transversum,  telen- 
cephalic  chorioid  plexus,  and  dorsal  arch.  None  of  these  show 
such  a  marked  tenacity  as  the  epiphyseal  complex,  a  fact  which 
but  serves  to  emphasize  the  significance  of  the  relative  constancy 
among  the  structures  derived  from  the  diencephalic  roof-plate. 

d.  Relative  constancy  of  the  several  parts  of  the  epiphyseal  com- 
plex, with  the  predominance  of  the  proximal  portion.     Since  each 
organ  of  the  epiphyseal  complex  presents  three  more  or  less 
well-defined  portions,  namely,  the  proximal  portion,  the  stalk, 
and  the  end- vesicle,  it  would  be  interesting  to  note  the  relative 
constancy  of  the  several  parts  in  the  phyletic  series  in  order  to 
ascertain,  if  possible,  which  of  these  is  the  most  fundamental 


212  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

element  in  the  complex.  Both  organs  are  well  developed  in 
cyclostomes.  The  proximal  portion  of  the  pineal  organ,  al- 
though present,  is  not  conspicuous,  but  it  is  doubtful  whether 
any  structure  which  may  be  designated  a  proximal  portion  can 
be  discerned  in  the  parapineal  organ.  The  stalks  and  end- 
vesicles  are  present  and  highly  specialized.  The  stalks  have 
lost  their  original  lumina  and  consist  of  two  sets  of  nerve  fibers. 
Both  end- vesicles  are  well  differentiated. 

In  selachians  the  parapineal  organ  is  entirely  absent.  The 
proximal  portion  of  the  pineal  organ  is  well  marked,  its  stalk  is 
long  and  hollow,  and  its  end- vesicle  a  dilated  sac. 

In  ganoids  and  teleosts  the  parapineal  organ  is  rudimentary; 
in  the  embryo  it  presents  a  small  proximal  portion  which  subse- 
quently becomes  much  reduced  in  size,  rendering  it  difficult  of 
recognition  in  the  adult.  The  stalk  is  short  and  slender  and  con- 
tains no  lumen.  The  end- vesicle  is  very  small.  The  proximal 
portion  of  the  pineal  organ  shows  a  considerable  dilatation  and 
is  connected,  by  means  of  a  hollow  stalk,  with  an  extensive 
end-vesicle. 

In  amphibia  the  parapineal  organ  is  absent.  The  proximal 
portion  of  the  pineal  organ  is  a  large,  dilated  sac  whose  lumen 
communicates  with  the  third  ventricle.  The  stalk  is  reduced  to 
a  slender  nerve  strand  extending  from  the  free  extremity  of 
the  proximal  portion  to  the  end-vesicle  which  lies  immediately 
beneath  the  skin  in  the  region  of  the  head. 

In  the  primitive  reptiles,  including  sphenodon  and  lacertilia, 
the  parapineal  organ  is  present  and  shows  a  marked  development. 
In  the  embryo  there  is  a  prominent  proximal  portion,  which, 
however,  becomes  gradually  reduced  hi  size,  and  in  the  adult  is 
difficult  to  distinguish.  The  stalk  of  the  parapineal  organ 
presents  itself  in  the  form  of  a  long  slender  fasciculus  of  nerve 
fibers  which  connects  the  superior  commissure  with  an  end- 
vesicle.  The  pineal  organ  shows  a  highly  specialized  proximal 
portion  which  is  large  and  convoluted.  Its  cavity  communicates 
with  the  third  ventricle  through  a  narrow  canal.  The  stalk  is 
short  and  contains  a  cavity  which  communicates  with  the  end- 
vesicle  at  its  distal  extremity  and  also  with  the  proximal  por- 


THE    PINEAL   BODY  213 

tion.  In  ophidians  and  chelonians  the  parapineal  organ  is 
entirely  absent,  and  the  only  element  of  the  pineal  organ  which 
persists  is  the  proximal  portion  which  has  become  converted  into 
a  more  or  less  solid  structure  extending  from  the  roof  of  the  brain 
dorsad  toward  the  vault  of  the  skull.  Similarly,  in  birds  and 
mammals,  the  only  element  of  the  epiphyseal  complex  which 
may  be  recognized  is  the  proximal  portion  of  the  pineal  organ. 
This,  as  in  reptiles,  is  an  organ  of  considerable  density  close  to 
the  roof  of  the  brain. 

From  these  facts  it  will  be  seen  that  the  proximal  portion  of 
the  pineal  organ  is  the  most  constant  element  of  the  epiphyseal 
complex,  the  next  in  point  of  frequency  being  the  end-vesicle 
and  stalk  of  the  pineal  organ.  •  It  would  seem,  therefore,  that  the 
proximal  portion  of  the  pineal  organ  should  be  considered  the 
fundamental  element  of  the  epiphyseal  complex,  and  its  struc- 
ture would,  therefore,  demand  particular  attention.  That  this 
element  in  the  epiphyseal  complex  does  show  a  marked  tendency 
toward  specialization  from  the  selachians  to  reptiles,  birds  and 
mammals  is  convincing  evidence  that  this  structure  is  not  to  be 
considered  a  vestige,  for  were  such  the  case  it  would  scarcely 
manifest  such  a  definite  tendency  toward  specialization  in  the 
processes  of  evolution. 

e.  The  epiphy so-cerebral  index.  Not  alone  is  the  evidence 
obtained  from  the  comparative  studies  of  the  pineal  body  in 
favor  of  its  progressive  specialization,  but  quite  as  much  the 
facts  obtained  from  ontogenesis  of  the  organ  in  man.  We  are 
fortunate  to  possesss  a  careful  series  of  observations  made  by 
Cut  ore76  in  which  the  weight  of  the  brain  as  well  as  the  weight 
of  the  epiphysis  and  the  hypophysis  have  been  recorded.  These 
statistics  are  based  upon  the  observations  ranging  from  the  new- 
born to  the  seventieth  year  of  life.  In  all,  twenty-five  brains 
were  studied,  and  it  would  seem  that  from  such  material,  limited 
though  it  may  be,  some  light  might  be  shed  upon  the  ontogenetic 
evolution,  upon  the  epiphysis  in  its  relation  to  the  rest  of  the 
brain  and  also  to  a  recognized  endocrinal  organ,  the  hypophysis, 

If,  as  has  been  frequently  maintained,  the  pineal  body  is  a 
vestige  and  of  no  functional  significance,  then  the  tendency  for 


214 


FREDERICK    TILNEY   AND    LUTHER    F.    WARREN 


this  organ  should  be  to  manifest  the  signs  of  regression  through 
the  periods  of  growth  in  man.  Or  if,  on  the  other  hand,  as  is 
thought  to  be  the  case  by  many,  the  organ  is  functional  only 
in  the  fetal  and  in  the  early  postnatal  stages,  then  the  relative 
weight  of  the  organ  to  the  rest  of  the  brain  should  show  an 
alteration  in  its  ratio,  indicating  a  progressive  retrograde  process 
taking  place  in  its  structural  elements. 

In  preparing  the  figures  of  Cutore,  in  order  most  effectively  to 
assemble  the  facts  necessary  to  this  argument,  his  cases  were 
grouped  in  such  a  way  as  to  constitute  five  more  or  less  well- 
defined  epochs  of  life. 

1.  Six  examples  of  infants  in  the  first  year. 

2.  Five  examples  of  infants  in  the  second  year. 

3.  Six  examples  of  children  from  3  to  14  years. 

4.  Five  examples  of  adults  from  15  to  25  years. 

5.  Three  examples  of  adults  from  60  to  70  years. 


AVERAGE  WEIGHT  IN  GRAMS 

INDEX  TO  BRAIN 

Epoch 

Brain 

Hypophysis 

Epiphysis 

Hypophysis 

Epiphysis 

1st 

600 

0.103 

0.031 

0.00017 

0.00005 

2nd 

734 

0.154 

0.055 

0.407 

0.00007 

3rd 

1,105 

0.262 

0.100 

0.00024 

0.00009 

4th 

1,218 

0.508 

0.119 

0.00040 

0.00009 

5th 

1,125 

0.500 

0.130 

0.00040 

0.00010 

It  will  be  seen  from  these  figures  that  of  the  "three  structures, 
considered,  the  average  weight  of  the  epiphysis  alone  tends  to 
increase  constantly  through  the  five  epochs  differentiated  in 
this  study.  The  brain  itself  shows  a  constant  increment  in 
weight  from  the  first  year  to  and  through  the  twenty-fifth  year, 
but  in  the  fifth  epoch,  from  sixty  to  seventy  years,  there  is  an 
apparent  decrease  of  nearly  100  grams  in  brain  weight.  The 
increase  in  the  hypophysis  runs  parallel  to  that  of  the  brain, 
for  up  to  the  fourth  epoch  and  including  it  the  increment  in 
weight  in  the  hypophysis  is  constant,  but  in  'the  fifth  epoch, 
from  sixty  to  seventy  years,  the  figures  seem  to  indicate  a  defi- 
nite decrease  in  weight.  The  indices  expressing  the  epiphyso- 


THE    PINEAL   BODY  215 

cerebral  and  hypophyso-cerebral  ratio  bear  out  this  observa- 
tion and  definitely  indicate  an  increase  in  the  proportion  between 
the  brain  and  the  epiphysis  from  the  first  year  of  life  to  the 
fifth  epoch,  between  sixty  and  seventy  years.  If  compared  with 
the  conditions  observed  in  a  definitely  known  endocrinic  organ, 
the  hypophysis,  it  will  be  observed  that  in  the  first  period  the 
weight  of  the  pineal  bcdy  is  30  per  cent  of  the  hypophysis;  in 
the  second  epoch  it  is  also  30  per  cent;  in  the  third  epoch  it  is 
35  per  cent,  an  increase  which  is  of  much  importance  and  inter- 
est in  this  connection,  since  it  is  the  general  supposition  that  the 
gland  has  its  greatest  functional  activity  during  this  time  of 
life.  In  the  fourth  epoch  the  epiphysis  is  22  per  cent  of  the  hypo- 
physeal  weight,  while  in  the  fifth  epoch  it  is  25  per  cent. 

It  should  be  borne  in  mind,  while  considering  these  figures , 
that  the  hypophysis  is  a  compound  organ,  being  made  up  of  a 
neural  portion  in  addition  to  an  element  derived  from  the  oral 
ectoderm.  Its  greater  weight,  therefore,  is  in  part,  at  least, 
explained  by  its  non-glandular  neural  portion,  and  its  total 
glandular  weight  would  be  represented  by  a  fraction  only  of  this, 
total.  In  this  light,  the  proportion  between  the  epiphysis  and 
the  hypophysis  would  be  materially  changed,  and  while  it  is 
impossible  to  say  exactly  what  ratio  the  neural  portion  of  the 
hypophysis  bears  to  the  glandular  portion,  it  would  be  safe  to 
assume  that  the  proportion  is  as  1:2. 

From  this  standpoint,  the  figures  concerning  the  epiphysis 
assume  more  definite  significance  and  would  seem  to  point 
strongly  to  the  supposition  that  an  organ  destined  to  become 
regressive  would  scarcely  keep  pace  so  constantly  in  its  weight 
increment  with  an  organ  like  the  hypophysis  of  known  endo- 
crinic function.  The  figures  cited  are  suggestive  in  another 
sense,  namely,  they  would  seem  to  show  that  the  activity  of  the 
pineal  organ,  should  such  be  accredited  to  it,  does  not  cease  at 
any  particular  period  of  life,  and  that  while  there  may  be  reason 
to  believe  that  the  greatest  functional  activity  is  present  in  the 
third  epoch,  between  the  third  and  fifteenth  years,  there  are 
good  reasons  to  believe  that  the  organ  does  not  cease  to  perform 
its  functions  even  up  to  the  time  of  old  age. 


216  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

/.  Resistance  to  the  encroachment  of  the  corpus  callosum.  An- 
other characteristic  in  the  ontogenesis  of  the  epiphysis,  especially 
in  mammals,  speaks  against  the  possibility  of  its  being  a  vestige 
and  indicates  in  it  a  tenacity  as  a  morphologic  structure  so 
marked  as  to  suggest  the  probability  of  some  inherent  functional 
activity.  With  the  advent  of  the  commissural  fibers  whose  mas- 
sive collection  goes  to  make  up  the  corpus  callosum,  the  mam- 
malian brain  takes  on  a  character  not  observed  in  the  lower 
forms.  The  gradual  extent  of  this  great  'interhemispheral  com- 
missure in  a  caudal  direction  subjects  the  entire  roof  of  the 
diencephalon  to  new  conditions.  The  influence  of  these  new 
conditions  is  readily  seen  in  the  flattening  of  the  dorsal  sac  and 
the  reduction  of  the  paraphyseal  arch.  Yet,  even  in  the  in- 
stances in  which  the  corpus  callosum  extends  far  enough  caudad 
to  reach  the  midbrain,  the  epiphysis  withstands  its.  encroach- 
ment and  gives  evidence  of  a  resistive  adaptation  against  the 
pressure  of  the  new  structure.  It  seems  fair  to  presume  that  if 
there  were  vested  in  the  pineal  body  an  inherent  tendency  to 
retrograde,  under  the  pressure  of  this  newly  developed  mam- 
malian structure  which  has  so  uniformly  altered  the  configura- 
tion of  other  elements  in  the  diencephalic  roof-plate,  the  epiphysis 
itself  must  have  given  evidence  of  much  less  resistance  or  per- 
haps have  Succumbed  altogether.  Its  evident  effort  at  adapta- 
tion has  already  been  referred  to  in  the  classification  of  the 
epiphysis  in  mammals  which,  according  to  Cutore,76  shows  a 
disposition  on  the  part  of  the  organ  to  accommodate  itself  to 
the  presence  of  the  corpus  callosum,  in  some  forms  being  retro- 
callosal  in  position,  in  others  supracallosal,  and  still  again  main- 
taining itself  in  all  its  morphologic  intactness  in  a  distinctly 
subcallosal  position. 

If  the  epiphysis  is  to  be  considered  a  vestige,  in  view  of  the 
morphologic  evidence  above  summarized,  it  seems  apparent 
that  the  burden  of  proof  rests  with  those  making  the  claim  that 
it  is  a  rudimentary  structure.  To  maintain  this  position  they 
must  meet  with  some  well-sustained  objections  the  following 
established  facts: 


THE    PINEAL   BODY  217 

1.  The  phyletic  constancy  of  the  epiphysis. 

2.  Its  phyletic  variations  and  morphologic  specializations. 

3.  Its  relatively  greater  phyletic  constancy  with  reference  to 
other  structures  in  the  pineal  region. 

4.  The  phyletic  predominance  of  the  proximal  portion  of  the 
pineal  organ. 

5.  The  evidence  of  its  progressive  specialization  in  ophidians, 
birds,  and  mammals. 

6.  The    increase    of    the    epiphy  so-cerebral    index    from    the 
earliest  stages  to  the  latest  periods  of  life  in  man. 

7.  The  resistance  to  the  encroachment  of  a  prominent  neo- 
morph  in  the  mammalian  brain  such  as  is  the  corpus  callosum, 
whose  presence  has  produced  such  a  marked  alteration  in  the 
other  constitutents  of  the  diencephalic  roof-plate. 

3.  Evidence  based  on  the  'histology  of  the  epiphy  seal  complex 

From  the  comparative  histology  of  the  epiphyseal  complex, 
it  becomes  evident  that  specialization  in  these  organs  has  fol- 
lowed two  main  lines:  First,  the  structures  have  either  differ- 
entiated in  the  interest  of  forming  visual  organs  or,  second, 
they  have  given  rise  to  glandular  itissue.  In  some  instances, 
both  of  these  tendencies  may  be  observed,  that  is  to  say,  in 
certain  species  the  differentiation  has  been  in  the  interest  of 
visual  apparatus  in  one  part  of  the  epiphyseal  complex,  while  in 
another  part,  distinct  glandular  tendencies  are  apparent.  It 
seems  advisable  for  the  purpose  of  obtaining  as  comprehensive  a 
view  as  possible  of  the  histology  of  this  portion  of  the  brain  to 
consider  the  leading  features  of  the  finer  structure  in  the  pineal 
body  of  each  of  the  classes  of  vertebrates. 

Histological  evidence  in  cyclostomes.  The  striking  histological 
features  in  cyclostomes  are  the  specializations  in  both  pineal  and 
parapineal  organs  in  the  interest  of  forming  visual  structures. 
The  end-vesicle  of  the  parapineal  as  well  as  the  pineal  organ 
presents  a  retina.  This  structure  in  the  pineal  organ  contains 
cells  of  a  distinct  rod-like  shape  which  have,  therefore,  been 
designated  the  rod  cells.  Other  cellular  elements  are  also  .ob- 


218  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

served  in  the  ventral  wall  of  the  end-vesicle  which  appear  to  be 
of  a  sensory  nature.  Certain  large  elements  have  been  recog- 
nized in  the  deeper  layers  of  the  tissue  and  by  some  authorities 
are  considered  to  be  ganglionic  cells.  In  addition,  there  are  cells 
of  an  ependymal  nature  or  modifications  of  the  latter  which  give 
the  impression  of  neuroglia  tissue.  There  can  'be  little  question 
that  the  retina  of  this  organ  is  well  enough  defined  to  deserve 
that  designation.  Whether  it  is  actually  functional  as  a  visual 
organ  is  not  altogether  clear,  for  the  relation  of  the  pineal  eye  in 
cyclostomes  to  the  surface  of  the  head  does  not  afford  the  most 
advantageous  conditions  for  a  distance  receptor. 

The  end-vesicle  of  the  parapineal  organ  closely  resembles  the 
finer  structure  in  the  corresponding  part  of  the  pineal  organ. 
There  are,  however,  certain  differences  which  are  more  those  of 
degree  than  of  kind.  The  rod  cells,  such  conspicuous  elements 
in  the  pineal  organ,  are  less  well  defined  in  the  parapineal  organ 
and  so  also  are  the  ganglionic  cells. 

The  differentiation  of  the  dorsal  wall  of  the  end-vesicle  in  the 
pineal  as  well  as  in  the  parapineal  organ 'manifests  a  tendency 
toward  lens  formation,  for  in  both  cases  the  cells  in  this  region 
are  entirely  pigment-free  and  give  rise  to  a  translucent  structure 
known  as  the  pellucida. '  Further  evidence  of  the  visual  adapta- 
tion observed  in  the  end-vesicle  of  the  two  structures  of  the 
epiphyseal  complex  is  the  fact  that  the  cavity  of  the  vesicle  is 
filled  with  a  coagulum  in  the  meshes  of  a  delicate  syncytium,  a 
structure  which  so  closely  resembles  a  primitive  vitreous  that  it 
may  be  regarded  as  analogous,  if  not  homologous  to  that  struc- 
ture. The  presence  in  the  retina  of  a  widely  distributed  white 
pigment  lends  the  necessary  opacity  to  the  visual  membrane. 
Both  end-vesicles  contain  this  pigment;  its  presence  serves 
further  to  convey  the  impression  of  differentiation  along  visual 
lines. 

The  stalks  of  both  the  pineal  and  parapineal  organs  bear  a 
certain  amount  of  confirmatory  evidence  in  favor  of  the  belief 
that  the  epiphyseal  complex  in  cyclostomes  has  made  the  at- 
tempt at  visual  adaptation.  Nerve  fibers  are  uniformly  ob- 


THE    PINEAL    BODY  219 

served  in  the  stalks;  those  coming  from  the  pineal  end-vesicle 
terminate  in  the  posterior  commissure,  while  those  seemingly  in 
connection  with  the  parapineal  end-vesicle  end  in  the  habenular 
commissure.  Some  collateral  evidence  is  afforded  by  the  appear- 
ance of  a  parietal  cornea,  a  fiberless  tissue  which  surrounds  the 
pineal  and  parapineal  end-vesicles. 

All  of  these  histological  facts,  based  upon  the  observation  of 
cyclostomes,  indicate  what  may  be  considered  an  abortive  yet 
a  well-advanced  attempt  to  the  formation  of  two  eyes.  There 
is  no  evidence  of  glandular  formation  in  any  part  of  the  epi- 
physeal  complex  in  cyclostomes. 

Histological  evidence  in  selachians.  The  characteristics  of  finer 
structures,  so  conspicuous  in  petromyzon  and  its  congeners,  is 
strikingly  absent  in  the  next  higher  order,  the  selachians.  In 
consequence  of  the  apparent  lack  of  differentiation,  the  entire 
parapineal  organ  is  absent,  while  the  pineal  organ,  although 
conspicuous  for  its  size,  shows  no  tendency  toward  the  formation 
of  a  retina,  pellucida,  white  pigment,  or  nerve  fibers.  It  is  a 
question  whether  the  pineal  organ  in  selachians  should  be  con- 
sidered as  a  primitive  organ  or  as  one  in  a  stage  of  retrogression. 
The  walls  of  the  end-vesicle  are  made  up  exclusively  of  epen- 
dymal  cells  and  contain  neither  spindle  nor  rod  cells.  In  one 
form,  Scyllium,  Galeotti140  described  a  peculiar  appearance  of 
the  cells  of  the  end-vesicle  which  seemed  to  indicate  a  secretory 
function.  This  conclusion  of  Galeotti's  depends  on  the  appear- 
ance of  fuchsinophile  granules  not  only  in  the  nuclei  of  the  cells, 
but  scattered  diffusely  throughout  the  cytoplasm.  Studnicka391 
also  recognized  these  cells  and,  while  he  was  unwilling  to  attrib- 
ute any  definite  function  to  them,  he  was  of  the  opinion  that  they 
could  not  be  secretory  in  their  nature. 

It  is  apparent,  therefore,  in  passing  from  the  cyclostomes  to 
the  selachians  that  there  is  a  striking  absence  of  any  visual 
differentiation  or  any  tendency  in  this  direction,  while  the 
presence  of  certain  histological  characters  in  the  cells  furnishes 
evidence  pointing  to  a  possible  glandular  formation  in  the  end- 
vesicle  of  the  pineal  organ. 


220  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

Histological  evidence  in  ganoids.  The  pineal  organ  alone 
develops  in  ganoids,  although  in  a  single  form,  namely,  Amia, 
an  abortive  parapineal  organ  makes  its  appearance.  The  end- 
vesicle  of  the  pineal  organ  in  ganoids  generally  shows  some 
tendency  toward  the  development  of  a  retinal  or  pellucidal 
layer,  although  neither  of  these  is  well  marked.  Studnicka,391 
as  the  result  of  his  studies  upon  ganoids,  does  not  believe  that 
there  is  any  evidence  of  glandular  activity  in  the  end-vesicle 
or  proximal  portion  which  is  at  all  comparable  to  that  of  the 
corresponding  parts  in  selachians.  On  the  other  hand,  he  does 
not  deny  that  there  may  possibly  be  secretory  function  in  the 
pineal  organ  of  ganoids. 

Histological  evidence  in  teleosts.  The  epiphyseal  complex  in 
teleosts  differs  from  that  in  selachians  and  ganoids  in  being  a 
much  larger  structure.  The  end-vesicle,  furthermore,  mani- 
fests, in  nearly  every  species,  a  pronounced  tendency  toward  the 
convolution  of  its  walls.  Not  only  is  this  process  apparent 
upon  the  surface,  but  section  of  the  vesicle  shows  it  to  consist 
of  many  folds  and  diverticula,  all  of  which  give  to  it  the  appear- 
ance of  a  tubular  gland  in  communication  with  the  third  ven- 
tricle by  means  of  a  long  hollow  stalk.  Galeotti140  in  Leuciscus 
found  evidence  of  secretory  activity  in  the  presence  of  fuch- 
sinophile  granules  similar  to  those  described  by  him  in  selach- 
ians. The  product  of  this  secretion,  he  thinks,  is  delivered  to 
the  lumen  of  the  end-vesicle  and  thus  to  the  ventricle  of  the 
diencephalon.  Studnicka391  observed  cells  having  a  similar 
appearance,  and  although  he  did  not  commit  himself  definitely 
as  to  their  nature,  he  nevertheless  expressed  the  belief  that  the 
organ  is  not  entirely  a  gland.  Some  nerve  fibers  of  the  stalk 
seem  to  represent  a  rudimentary  pineal  nerve. 

Histological  evidence  in  amphibia.  The  first  recognition  and 
description  given  by  Stieda379  in  which  he  called  the  end-vesicle 
a  frontal  subcutaneous  gland  was  evidently  a  misinterpretation 
of  the  conditions  in  amphibia.  The  end- vesicle  in  these  animals 
is  fairly  well  developed,  presenting  a  retina  and  lens  which, 
although  clearly  recognizable  as  such,  have  attained  scarcely 
more  than  an  abortive  state  in  their  development.  A  long 


THE    PINEAL   BODY  221 

slender  stalk  made  up  almost  exclusively  of  nerve  fibers  con- 
nects this  organ  with  the  tip  of  the  proximal  portion  arid  con- 
stitutes a  nervus  pinealis,  in  the  strict  sense,  which  terminates  in 
the  posterior  commissure.  Galeotti140  in  Spelerpes  fuscus 
observed  evidence  of  secretory  activity,  and  this  he  also  found  in 
Bufo  and  Rana.  The  evidence  of  secretory  activity  depended 
upon  the  appearance  of  fuchsinophile  granules  in  the  cytoplasm. 
'Studnicka,391  following  Galeotti,  found,  as  he  had  previously 
observed  in  selachians  and  teleosts,  many  cells  in  adult  amphibia 
containing  cytoplasmic  granules.  These  he  interpreted  as  cells 
having  a  sensory  nature.  Galeotti  based  his  belief  of  secretory 
activity  in  the  pineal  organ  not  merely  upon  the  presence  of 
fuchsinophile  granules,  but  quite  as  much  upon  epithelial  char- 
acters of  the  cells  which  were  arranged  in  alveoli,  thus  giving 
the  end- vesicle  and  the  proximal  portion  a  glandular  appearance. 

It  is  apparent  from  this  evidence  that  amphibia  in  general 
present  a  very  abortive  attempt  toward  the  formation  of  retinal 
and  lenticular  structures,  while  the  end-vesicle  and  the  proximal 
portion  of  the  pineal  organ  both  show  some  evidence  of  glandu- 
lar formation. 

Histological  evidence  in  reptilia.  The  finer  structure  of  the 
epiphyseal  complex  in  the  primitive  reptiles,  including  Spheno- 
don  and  lacertilia,  shows  that  in  these  forms  the  parapineal 
organ  attains  its  highest  differentiation  as  a  visual  structure. 
The  pineal  organ,  however,  shows  no  tendency  whatsoever  in 
this  direction,  while,  on  the  other  hand,  its  proximal  portion 
affords  many  indications  that  its  differentiation  has  been  along 
glandular  lines.  In  ophidia  and  chelonia  the  proximal  por- 
tion of  the  pineal  organ  alone  persists  and  has  the  appearance 
of  a  highly  vascular,  richly  branched,  tubular  gland.  The 
structure  generally  known  as  the  pareital  eye  is  a  prominent 
morphological  feature  in  primitive  forms  of  reptiles.  It  is 
absent  in  certain  geckonidae  and  in  a  number  of  agamidae.  It 
attains  its  greatest  differentiation  in  Sphenodon  and  here  pre- 
sents a  well  marked  retina,  lens,  vitreous,  cornea,  and  nerve,  the 
latter  relating  to  the  ganglion  habenulae.  The  accessory  struc- 
tures related  to  the  parietal  eye,  including  the  cornea,  parietal 


222  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

fossa,  and  parietal  spot,  all  give  evidence  of  the  most  complete 
adaptation  for  visual  function. 

Studnicka391  believes  that  the  rich  capillary  blood  supply  in 
ophidia  speaks  in  favor  of  the  glandular  nature  of  the  organ, 
its  secretion  being  contributed  to  the  blood  stream.  In  chelonia 
the  cellular  elements  are  mostly  ependymal  and  neurogliar  and 
no  nerve  cells  or  nerve  elements  are  found.  There  is,  however, 
no  clear  evidence  of  the  secretory  nature  of  the  epiphyseal  com-' 
plex  in  these  forms. 

The  conclusions  which  may  be  drawn  with  reference  to  reptiles 
seem  to  indicate  that  in  the  primitive  forms  the  parapineal  organ 
assumes  the  highest  differentiation  which  it  attains  as  a  visual 
structure.  There  is  some  evidence  that  the  pineal  organ,  even 
in  the  animals,  manifests  a  tendency  toward  glandular  forma- 
tion. In  ophidians,  however,  there  can  scarcely  be  a  doubt 
that  the  proximal  portion  of  the  pineal  organ  is  the  only  element 
which  persists  and  that  it  has  a  definitely  glandular  structure. 
This  is  probably  true  also  in  chelonians.  The  pineal  gland  in  the 
snake  and  turtle  probably  contributes  its  secretion  to  the  blood 
stream,  but  may  also  impart  a  portion  of  it  to  the  cerebrospinal 
fluid.  The  more  recent  reptiles  manifest  no  disposition  on  the 
part  of  the  epiphyseal  complex  to  develop  any  sensory  or  other 
type  of  neural  mechanism. 

Histological  evidence  in  birds.  The  conspicuous  change  in  the 
epiphyseal  complex  noted  in  the  transition  from  the  primitive 
reptiles  to  those  of  more  recent  history  is  strikingly  emphasized 
when  the  condition's  in  this  region  of  the  brain  in  birds  are 
reviewed.  Here,  as  in  the  snakes  and  turtles,  there  is  com- 
plete suppression  of  the  parapineal  organ,  and  that  tendency 
toward  the  differentiation  of  a  visual  apparatus  which  seems  to 
have  reached  its  height  in  Sphenodon,  has  so  far  receded  as  to 
leave  no  indication  in  birds  of  its  earlier  existence.  This  histo- 
logical  feature  of  itself  is  highly  significant,  but  when  taken  in 
conjunction  with  the  appearance  offered  by  the  finer  structure  of 
the  pineal  body  in  birds,  it  seems  to  set  all  doubt  aside  as  to  the 
inherent  tendency  of  the  epiphyseal  complex  along  its  major 
lines  of  differentiation.  In  every  species  of  birds  which  has  so 


THE    PINEAL   BODY  223 

far  come  under  observation,  the  differentiation  in  the  pineal 
body  has  been  in  the  interest  of  glandular  formation.  This 
evidence  is  not  alone  to  be  found  in  the  character  of  the  cells 
which  compose  the  body,  but  even  more  in  the  arrangement  of 
these  cells  whose  alveolar  patterns  constitute  irrefutable  reasons 
for  regarding  the  epiphysis  as  a  true  gland  in  birds. 

Three  types  of  this  gland  are  found  in  the  avian  forms,  namely, 
1)  the  tubular  type,  in  which  the  secretion  is  delivered  to  the 
ventricular  system;  2)  the  endocrinic  type,  in  which  the  secre- 
tion reaches  the  blood  stream,  and  3),  a  mixed  type,  partaking 
of  the  character  of  each  of  the  former  varieties.  This  evidence 
afforded  by  birds  is  so  conclusively  in  favor  of  the  glandular 
nature  of  the  epiphysis  as  to  leave  no  grounds  for  dispute. 

Histological  evidence  in  mammals.  It  is  perhaps  in  mammals 
that  the  most  extensive  observations  have  been  made  with 
reference  to  the  histology  of  the  pineal  body.  Indeed,  it  is  in 
these  animals  that  the  greatest  variety  of  opinion  has  been 
expressed.  It  would  seem  advisable  to  take  into  account  these 
different  views  concerning  the  histological  character  of  the  organ. 
A  large  group  of  investigators  adheres  to  the  belief  that  the 
pineal  body  is  a  blood  vascular  gland.  This  group  includes, 
among  others,  Valentin,403  Faivre,114  Leydig,231  Bizzozero,31 
Galeotti,140  Constantini,71  Cutore,76  Galasescu-Urechia,137 
Krabbe,217  Biondi,49  and  Kidd.203  Jordan,199  although  he  does 
not  advocate  the  improbability  of  glandular  formation,  believes 
that  the  organ  is  essentially  neural  in  its  structure. 

Several  investigators  maintain  that  the  epiphysis  in  mammals 
consists  exclusively  of  neuroglia.  Among  these  are  Cionini,66 
Edinger,103  and  Weigert.418  Mihalkovicz274  believed  that  the 
cellular  consistency  of  the  pineal  body  in  mammals  was  exclu- 
sively of  the  ependymal  type.  Those  of  another  group  assert 
that  the  epiphysis  resembles  a  lymph  gland.  Of  this  opinion  are 
Schwalbe,348  Henle,171  Ellenberger110  Mingazzini,276  and  Lord.249 

Although  it  has  been  frequently  claimed  by  many  writers 
among  both  the  early  and  recent  workers  in  this  field  that  the 
epiphysis  is  a  vestige,  it  is  interesting  to  note  that  no  suggestion 
of  such  a  possibility  is  made  by  any  of  the  authorities  just 


224  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

cited.  This  is  of  particular  significance  because  this  list  in- 
cludes the  names  of  those  who  have  given  the  most  extensive 
attention  to  the  histological  character  of  the  epiphysis  in 
mammals.  Milhalkovicz'274  conception  of  the  histology  of  the 
pineal  body  seems  hardly  tenable,  for  it  requires  little  study 
covering  a  number  of  different  mammalian  forms  to  become  con- 
vinced that  the  cellular  elements  entering  into  the  epiphysis 
have  nothing  in  common  with  the  ependymal  cells.  Even 
though  it  may  be  admitted  that  a  certain  number  of  the  cellular 
constituents  of  the  epiphysis  are  ependymal  in  type,  it  cannot, 
in  the  light  of  our  present  knowledge,  be  held  that  the  organ  is 
made  up  exclusively  of  this  type  of  cells. 

On  the  other  hand,  it  13  not  possible  to  acceed  to  the  conten- 
tion of  those  who  uphold  the  idea  that  the  epiphysis  is  similar 
to  lymphatic  glands.  Not  only  does  the  character  of  the  chief 
cellular  elements  in  the  pineal  body  of  mammals  make  this 
position  seem  untenable,  but  even  more  does  the  arrangement 
of  these  cells  point  away  from  the  supposition  that  this  is  in 
any  sense  lymphoid  in  character.  Few  cells  in  the  body  are 
more  conspicuous  for  their  histological  character  than  the  chief 
or  parenchymatous  elements  of  the  mammalian  epiphysis. 
The  large  and  centrally  placed  nucleus,  the  extensive  and  glan- 
dular cytoplasm  mark  these  cells  so  definitely  that  they  may  be 
recognized  without  any  difficulty  even  in  those  instances  when 
they  become  ectopic  because  of  such  migration  as  not  infre- 
quently results  from  tumor  formation  in  the  pineal  body. 

Our  own  work  in  this  regard  is  illustrated  in  the  figures  which 
show  the  character  of  the  pineal  gland  cells  in  Macropus  grayi, 
Zalophus,  Camelus  dromedarius,  Capra  hylocrius,  Lepus,  Simia 
satyrus,  and  in  man.  Furthermore,  our  observations  in  the 
ontogenesis  of  the  epiphysis  in  Felis  domestica  and  in  man, 
illustrations  of  which  are  given  in  figures  91  and  92,  show  that 
in  the  early  stages  of  differentiation  the  nuclei  of  the  ependymal 
cells  are  so  large  and  the  cytoplasm  so  scanty  that  they  give 
the  impression  of  lymphoid  tissue,  but  in  the  later  stages  the 
cytoplasm  increases  so  considerably  in  amount  that  it  is  no 
longer  possible  to  conceive  of  these  cells  as  lymphoid  in  char- 


THE    PINEAL   BODY  225 

acter.  In  fact,  they  have  in  the  later  periods  of  fetal  and  early 
postnatal  life  all  the  appearances  usually  associated  with  glan- 
dular cells.  As  compared  to  the  cells  in  the  glandular  portion 
of  the  hypophysis,  the  size  of  the  pineal  cells  is  two  or  three 
times  as  great.  This  difference  in  size  affords  a  striking  point 
of  differentiation  in  those  pathological  conditions  in  which  the 
pineal  cells  in  the  course  of  tumor  formation  have  migrated  into 
and  through  the  posterior  lobe  of  the  hypophysis  and  invaded 
the  pituitary  gland.  The  contrast  is  so  marked  as  to  present 
no  difficulty  in  the  identification  of  the  two  varieties  of  cells. 
That  the  epiphysis  is  made  up  of  neuroglia  cells  in  large  part, 
if  not  entirely,  has  been  the  contention  of  several  observers. 
The  presence  of  short,  branching  fibers  in  close  proximity  to  the 
pineal  cells  has  seemed  to  be  the  basis  for  this.  On  the  other 
hand,  if  the  pineal  cells  in  mammals  are  to  be  regarded  as  neu- 
roglia, it  must  be  granted  that  they  are  certainly  unlike  the 
neuroglia  cells  observed  hi  other  parts  of  the  central  nervous 
system.  Dimitrova,92  who  makes  out  such  a  strong  case  from 
her  histological  study  in  favor  of  the  neuroglial  character  of  the 
epiphysis,  seems  to  base  her  conclusions  upon  criteria  which  are 
not  wholly  convincing,  for  the  mere  presence  of  demonstrable 
fibers  in  the  neighborhood  of  the  cells  does  not  of  itself  indicate 
that  these  cells  are  neuroglial  in  character.  Furthermore,  this 
view  neglects  to  take  into  account  the  highly  specialized  char- 
acter of  the  pineal  cells.  If,  on  the  other  hand,  it  be  granted 
that  the  cell  constituency  of  the  epiphysis  is,  in  major  part, 
neurogliar,  this  admission  would  not  wholly  invalidate  the  idea 
that  the  structure  is  glandular  in  nature,  for,  according  to  the 
most  recent  researches  of  Nageotte281  and  Ma  was,263  neuroglia 
cells  contain  mitochondria  and  hence,  according  to  these  inves- 
tigators, should  be  considered  as  glandular  elements.  In  this 
light,  the  neuroglia  throughout  the  entire  nervous  system  is 
endowed  with  secretory  function.  In  general,  however,  it 
does  not  seem  necessary  to  invoke  this  interpretation  of  the 
neuroglia  in  order  to  place  the  pineal  body  in  the  class  of  glan- 
dular structures,  for  the  character  of  the  pineal  cells  is  in  itself 
sufficient  argument  in  favor  of  a  function  different  from  that 


MEMOIR   NO. 


226  FREDERICK   TILNEY   AND    LUTHER    F.    WARREN 

attributed  to  neuroglia  in  the  ordinary  sense  and  most  in  favor 
of  a  glandular  activity. 

The  observations  of  Nicolas,283A  later  confirmed  by  Dimitrova,92 
in  which  muscle  cells  were  reported  as  histological  elements  of 
the  epiphysis  in  several  Ungulates,  have  not  been  confirmed  by 
any  other  observers,  and  some  authorities  have  been  categorical 
in  their  affirmation  concerning  the  absence  of  such  elements. 
That  the  epiphysis  may  contain  nerve  cells  and  nerve  fibers  is 
probable,  but  there  is  no  evidence  in  mammals  of  the  existence 
of  any  neural  mechanism  in  the  pineal  body. 

To  consider  the  epiphysis  in  mammalia  as  a  vestige  in  the 
light  of  the  histological  evidence  here  summarized  seems  to  be 
an  attitude  which  is  wholly  untenable,  all  the  more  so  when 
this  histological  evidence  points  to  the  fact  that  the  structure 
is  a  gland.  For  in  this  respect  not  only  is  the  character  of  the 
cells  significant,  but  their  arrangement  in  definite  acini,  the  rich 
vascular  network  about  these  acini,  and  the  trabeculation  by 
means  of  connective  tissue  which  gives  this  structure  the  appear- 
ance common  to  all  glands,  are  also  suggestive  of  this  fact. 

The  final  conclusion  to  be  drawn  from  the  histological  evidence 
in  the  epiphyseal  complex  of  vertebrates  would  seem  clearly  to 
indicate  that  this  structure  of  the  pineal  region  possesses  a 
pluripotentiality  whose  fundamental,  inherent  tendency  is  in 
the  interest  of  glandular  differentiation  and  that  in  a  few  in- 
stances, as  in  cyclostomes,  amphibia,  and  in  primitive  reptiles, 
the  parapineal  or  pineal  organ  may  become  further  differentiated 
in  the  interest  of  a  highly  specialized  sensory  mechanism  which 
has,  or  has  had,  visual  function. 

4.  The  relation  of  the  parietal  eye  to  the  pineal  body 

Much  of  the  difficulty  in  interpreting  the  relation  between 
the  parietal  eye  and  pineal  body  arises  from  a  confusion  in  the 
use  of  terms.  If  by  pineal  body  is  meant  the  epiphysis  as  it 
appears  in  mammals,  it  becomes  relatively  simple  to  discuss 
the  relation  between  this  structure  and  the  third  eye  of  verte- 
brates. It  may  perhaps  be  arbitrary  thus  to  limit  a  term  which 


THE    PINEAL   BODY  227 

has  not  always  been  restricted  to  the  sense  here  advocated,  and 
yet,  as  has  been  previously  pointed  out,  it  was  from  precisely 
the  conditions  in  mammals  that  the  descriptive  conception, 
pineal  body,  took  origin. 

The  theory  that  the  pineal  body  is  the  vestige  of  the  parietal 
eye  is  accepted  by  many.  According  to  this  view,  the  third 
eye  of  vertebrates  should  be  regarded  as  primordial  and  the 
pineal  body  an  arrested  development  in  the  attempt  to  reach 
such  differentiation.  The  evidence,  however,  is  by  no  means 
conclusive,  for,  as  has  previously  been  shown,  the  entire  epi- 
physeal  complex  springs  from  a  region  which  is  fundamentally 
glandiferous,  while  only  in  a  very  few  instances  is  a  tendency 
toward  sensory  differentiation  recognizable  in  it.  By  far  the 
great  majority  of  vertebrates  manifest  in  the  epiphyseal  complex 
no  tendency  whatsoever  toward  the  development  of  any  neural 
mechanism.  This  would  seem  to  indicate  that  the  tendency  for 
the  epiphyseal  complex  to  develop  visual  structures  is  a  secon- 
dary and  not  a  primordial  character.  Furthermore,  if  the 
pineal  body  was  in  any  true  sense  the  vestige  of  the  parietal 
eye,  it  would  seem  almost  inevitable  that  the  organ  should  con- 
tain remnants  indicative  of  visual  specialization.  The  absence 
of  such  evidence  at  least  raises  a  reasonable  doubt  that  the  pineal 
body  had  at  any  time  possessed  visual  function.  The  almost 
universal  absence  of  true  ganglionic  cells  as  well  as  the  lack  of 
nerve  fibers,  which  may  be  regarded  as  belonging  to  some  cate- 
gory other  than  those  of  the  sympathetic  system,  would  seem  to 
call  into-  question  the  possibility  of  the  pineal  body  ever  having 
participated  in  the  formation  of  a  neural  mechanism.  This  may 
be  considered  negative  evidence.  There  remains  to  be  men- 
tioned, however,  the  significant  fact  that  the  pineal  body  in  all 
of  the  higher  vertebrates  manifests  a  tendency  to  differentiate 
along  lines  which  cannot  be  interpreted  as  in  the  interests  of 
visual  function.  As  has  been  previously  shown,  the  differen- 
tiation which  does  occur  in  the  higher  reptiles,  birds,  and  mam- 
mals gives  rise  to  glandular  tissue.  From  these  facts  it  seems 
possible  to  conclude  that  the  pineal  body  is  not  a  vestige  of  the 
parietal  eye. 


228  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

The  supposition  advanced  by  Hertwig175  and  others  that  the 
pineal  process  in  birds  and  mammals  undergoes  metamorphoses 
which  give  rise  to  an  organ  of  a  glandular  or  follicular  structure 
has  little  to  support  it.  Peytoureau308B  maintained  that  in 
the  evolution  through  the  vertebrate  phylum  the  pineal  body 
has  become  partly  atrophic  and  partly  metamorphosed  in  such 
a  way  as  to  cause  a  modification  in  the  connection  with  the 
nerve  centers.  Ultimately,  it  has  taken  on  the  characters  of 
an  epithelial  organ,  in  fact,  a  highly  vascular  gland  represented 
in  the  higher  mammals  by  the  pineal  gland  and  its  peduncle. 
To  assume  that  an  actual  process  of  metamorphosis,  in  a  literal 
sense,  from  a  visual  organ  to  a  glandular  structure,  is  respon- 
sible for  the  differences  between  the  parietal  eye  and  the  pineal 
gland  seems  wholly  unsatisfactory.  If,  however,  this  view  has 
reference  to  a  deflection  in  the  ontogenetic  process,  as  a  result  of 
which  the  pineal  anlage  in  certain  forms,  instead  of  giving  rise  to 
a  visual  structure,  produces  a  gland,  there  may  be  some  justifi- 
cation of  ascribing  these  changes  to  metamorphosis.  Yet,  even 
in  this  sense,  to  attribute  the  differences  between  the  parietal 
eye  of  Sphenodon  and  the  pineal  gland  of  the  bird  to  such  an 
indefinite  process  of  alteration  does  little  more  than  apply  a 
term  to  the  process  without  offering  an  explanation  for  it. 

Certain  investigators,  among  them  Rabl-Ruckhard,322  Ahl- 
born,2  and  Spencer,368  regard  the  pineal  body  as  an  unpaired 
parietal  eye  which,  in  many  classes,  for  example,  reptiles,  appears 
to  be  tolerably  well  preserved,  but  in  most  vertebrates  is  in  a 
process  of  degeneration.  This  theory  goes  a  step  further  than 
that  which  regards  the  pineal  body  as  a  vestige.  According  to 
the  former  view,  the  pineal  differences  between  such  forms  as 
possess  a  parietal  eye  and  those  in  which  no  such  structure 
develops  are  attributed  to  a  process  of  degeneration,  while,  the 
latter  theory  ascribes  them  to  an  arrested  development.  Evi- 
dence of  degeneration  in  the  higher  vertebrates  is  difficult  to 
discern.  The  figures  already  cited  in  reference  to  the  human 
pineal  gland  (p.  158)  makes  it  hard  to  believe  that  a  retrograde 
process  is  present,  even  in  the  late  periods  of  life.  The  appear- 
ance of  brain  sand  in  itself  is  not  sufficient  to  justify  such  a  con- 


THE    PINEAL   BODY  229 

elusion.  Furthermore,  in  no  instance  is  there  the  slightest 
indication  that  the  pineal  body  in  the  higher  vertebrates  con- 
tains histological  elements  which  may,  in  any  sense,  be  regarded 
as  degenerated  products  of  the  visual  structures  in  the  parietal 
eye.  That  the  pineal  body  in  birds  and  mammals  may  be  inter- 
preted as  the  result  of  a  degenerative  process  affecting  the 
parietal  eye  seems  wholly  untenable  in  the  absence  of  any  con- 
vincing signs  of  such  degeneration  and  also  because  the  weight 
of  evidence  furnished  by  many  facts  indicates  'the  glandular 
nature  of  the  organ. 

It  is  interesting  in  this  connection  to  give  the  opinion  of 
Bashford  Dean,83  in  which  that  author  expresses  doubt  concern- 
ing the  connection  between  the  epiphysis  and  the  median  eye  of 
vertebrates. 

The  evidence  as  to  the  presence  primitively  of  a  median  eye  in  fishes 
is  certainly  far  from  satisfactory.  It  is  possible  that  fishes  and  am- 
phibia may  in  their  extant  forms  have  lost  all  definite  traces  of  this 
ancestral  (visual)  organ  on  account  of  some  peculiar  conditions  of  their 
aquatic  living.  On  this  supposition  evidence  of  its  presence  might  be 
sought  in  the  pineal  structures  of  the  earliest  palaeozoic  fishes,  whose 
terrestrial  kindred  and  probable  descendants  may  alone  have  retained 
the  living  conditions  which  fostered  its  functional  survival.  It  is  of 
interest,  accordingly,  to  find  that  in  a  number  of  fossil  fishes  the  pineal 
region  retains  an  outward  median  opening  whose  shape  and  position 
suggest  that  it  may  have  contained  an  optic  capsule.  If  the  median 
eye  existed  in  these  forms  it  may  well  have  been  passed  along  in  the 
line  of  descent  through  the  early  amphibia  (where  substantial  traces 
of  a  parietal  foramen  occur,  e.g.  Cricotus)  to  the  ancestral  reptiles. 

The  evidence  that  the  median  opening  in  the  head-shields  of  ancient 
fishes  actually  enclosed  a  pineal  eye  is  now  felt  by  the  present  writer 
to  be  more  than  questionable.  The  remarkable  pineal  funnel  of  the 
Devonian  Dinichthys  is  evidently  to  be  compared  with  the  median 
foramen  of  Ctenodus  and  Palaedophus,  but  this  can  no  longer  be  looked 
upon  as  having  possessed  an  optic  function,  and  thus  practically  renders 
worthless  all  the  evidence  of  a  median  eye  presented  by  fossil  fishes. 

It  must,  for  the  present,  be  concluded  accordingly  that  the  pineal 
structures  of  true  fishes  do  not  tend  to  confirm  the  theory  that  the 
epiphysis  of  the  ancestral  vertebrates  was  connected  with  a  median 
unpaired  eye.  More  probably  it  was  connected  with  the  inner vation 
of  the  sensory  canals  of  the  head. 

The  theory  that  the  epiphysis  in  the  true  fishes  is  connected 
with  the  innervation  of  the  sensory  canals  of  the  head  adds  a 


230  FREDERICK   TILNEY   AND    LUTHER    F.    WARREN 

new  interpretation  concerning  the  function  of  the  pineal  organ. 
It  is  not  our  purpose  to  discuss  this  hypothesis,  but  we  do  desire 
to  emphasize  the  improbability  of  the  pineal  body  in  higher 
vertebrates  being  the  vestige  of  any  neural  mechanism.  This 
opinion  is  based  on  the  general  absence  of  definitely  neural 
elements  in  the  pineal  gland  other  than  those  connected  with  the 
sympathetic  system. 

Terry392  in  Opsanus  could  find  no  evidence  to  support  Dean's 
supposition  that  the  epiphysis  of  true  fishes  is  connected  with 
the  innervation  of  the  sensory  canals  of  the  head.  He  was, 
moreover,  unable  to  discover  the  evidence  in  the  teleost  to  sup- 
port the  theory  that  the  pineal  body  is  an  ocular  organ  either 
degenerate  or  rudimentary. 

The  portion  of  the  epiphyseal  complex  which  becomes  special- 
ized as  the  eye-like  structure  of  the  lower  vertebrates  constitutes 
the  end-vesicle.  This  end-sac  may  be  part  of  the  pineal  or  of 
the  parapineal  organ,  depending  upon  the  form  in  which  it 
occurs.  In  every  instance  the  appearance  of  visual  element  j  is 
limited  to  the  end-vesicle.  Not  only  is  the  structure  notable 
for  the  eye-like  character  of  its  histological  elements,  but  it 
occupies  a  position  with  reference  to  the  brain  and  also  to  the 
skull  which  further  serves  to  distinguish  it.  Its  connection  with 
the 'roof  of  the  interbrain  is  by  means  of  an  attenuated  stalk, 
which  gives  the  entire  structure  the  appearance  of  a  long  append- 
age of  the  brain.  The  junction  of  the  stalk  with  the  roof  is 
usually  not  a  direct  one  since  the  connection  in  most  forms  is 
accomplished  through  the  proximal  portion.  These  several 
parts,  which  may  be  recognized  in  the  pineal  and  parapineal 
organs  of  certain  classes,  should  be  regarded  as  separate  mor- 
phologic entities.  The  proximal  portion  has  little  in  common 
with  the  end-vesicle.  Its  position  and  histological  characters 
mark  it  as  strikingly  different.  Its  only  actual  relation  with 
the  vesicle  is  one  of  continuity  through  the  stalk.  This  con- 
tinuity may,  in  some  cases,  be  almost  lost  or  maintained  only 
by  a  small  filament  of  nerve  fibers.  Such,  for  example,  is  the 
condition  in  amphibia,  a  class  which,  perhaps,  affords  the  most 
conspicuous  instance  of  the  morphologic  distinction  between  the 


THE    PINEAL   BODY  231 

end-vesicle  and  the  proximal  portion  of  the  pineal  organ.  Were 
it  not  for  a  slender  fasciculus  of  nerve  fibers  these  two  portions 
of  the  epiphyseal  complex  would  appear  as  independent  entities. 
As  it  is,  both  parts  are  well  differentiated  and  well  developed, 
one  as  an  eye-like  organ,  the  other  with  some  of  the  characters 
of  a  gland.  This  distinction  between  the  end-vesicle  and  prox- 
imal portion  should  not  be  underestimated.  It  not  only  shows 
how  remote  the  relationship  between  the  two  parts  may  be, 
but  also  gives  an  added  prominence  to  the  proximal  portion. 
This  latter  part  has  already  been  shown  to  be  the  most  constant 
element  in  the  epiphyseal  complex,  while  the  end-vesicle  is  much 
more  limited  in  its  occurrence. 

The  process  by  means  of  which  the  end-vesicle  and  proximal 
portion  of  the  pineal  organ  are  rendered  so  distinctive  in  amphibia 
takes  on  a  new  phase  in  Sphenodon  and  lacertilia.  In  these 
forms  the  necessity  for  the  end-vesicle  to  assume  visual  char- 
acters has  apparently  ceased,  and  this  structure  together  with 
the  stalk  is  evidently  in  a  state  of  involution.  The  contrary, 
however,  is  true  of  the  proximal  portion  which  has  taken  on 
not  only  more  conspicuous  dimensions,  but  also  more  pro- 
nounced glandular  characters.  In  the  ophidians,  in  birds,  and 
in  mammals  the  process  of  involution  in  the  end- vesicle  and 
stalk  has  been  carried  to  its  final  stage.  No  trace  of  the  end- 
vesicle  or  the  stalk  is  to  be  found  in  any  of  the  orders  above 
lacertilia.  The  proximal  portion,  on  the  other  hand,  in  ophidi- 
ans, birds,  and  mammals  gains  prominence  because  of  its 
glandular  structure. 

The  process  here  described  from  amphibia  to  mammals  clearly 
demonstrates  the  progressive  involution  of  the  eye-like  end- 
vesicle  and  the  gradual  ascendency  of  the  glandular  proximal 
portion.  At  one  end,  namely  in  amphibia,  the  end-vesicle  and 
proximal  portion  must  be  regarded  as  coordinate  in  prominence. 
At  the  other  end,  i.e.,  in  ophidia,  the  proximal  portion  is  pre- 
eminent because  of  the  disappearance  of  the  end-vesicle.  This 
phenomenon  can  best  be  interpreted  on  the  basis  of  a  pluri- 
potentiality  in  the  anlage  of  the  epiphyseal  complex,  of  such  a 
nature  that  the  adaptive  possibility  for  the  development  of  a 


232  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

parietal  eye  or  of  a  gland,  or  the  simultaneous  development  of 
both  of  these,  is  given  in  their  origin. 

According  to  this  conception,  it  is  not  possible  to  consider  the 
parietal  eye  as  primordial;  it  seems  far  more  likely  that  it  is  an 
adaptive  modification  developing  in  response  to  special  require- 
ments in  a  limited  number  of  forms.  The  proximal  portion,  on 
the  other  hand,  maintains  its  entity  with  such  marked  per- 
sistency throughout  the  series  that  it  seems  possessed  of  the  more 
primitive  characters.  This  is  emphasized  when  the  proximal 
portion  is  considered  in  connection  with  the  other  glandular 
derivatives  of  the  diencephalic  roof.  Embryologically,  in  those 
instances  in  which  both  an  eye-like  end- vesicle  and  a  glandular 
proximal  portion  develop  the  anlage  of  these  parts  must  have 
been  pluripotential.  This  is  equally  true  in  the  instances  in 
which  one  portion  of  the  epiphyseal  complex,  as,  for  example,  the 
parapineal  organ,  develops  an  eye-like  structure  while  the 
pineal  organ  develops  a  marked  tendency  to  glandular  formation. 
Such  an  interpretation  of  the  pluripotentiality  in  the  epiphyseal 
anlage  when  applied  to  the  various  orders  reveals  the  following 
conditions : 

In  cyclostomes  the  epiphyseal  anlage  seems  to  contain  ele- 
ments which  are  exclusively  engaged  in  the  differentiation  of 
eye-like  structures  which  form  the  pineal  and  parapineal  eyes. 

In  selachians,  ganoids,  teleosts,  and  dipnoians  the  epiphyseal 
anlage  has  completely  lost  its  potentiality  to  differentiate  as  a 
visual  organ,  and  while  there  may  be  some  debate  as  to  the 
character  of  the  adult  structures,  there  is  some  evidence  which 
points  to  their  glandular  nature. 

In  amphibia  both  potentialities  are  present  in  the  pineal 
organ.  In  Sphenodon  and  lacertilia  both  potentialities  are  also 
present,  but  in  these  instances  the  parapineal  portion  of  the 
epiphyseal  complex  gives  rise  to  the  eye-like  structure  while  the 
pineal  portion  develops  glandular  characters.  In  ophidians  and 
all  the  higher  vertebrates  the  potentiality  for  the  development 
of  visual  structures  is  lost. 

Even  accepting  the  probability  of  this  dual  potentiality,  it 
should  be  borne  in  mind  that  the  median  eye-like  structure  may 


THE    PINEAL   BODY  233 

in  no  instance  signify  a  functionally  active  visual  organ.  In  all 
cases  the  attempt  to  develop  a  median  eye  may  represent  but 
the  abortive  and  partially  attained  differentiation  of  far  remote 
primitive  ancestors  in  which  such  an  eye  was  functionally  active. 
Its  persistence  into  extant  forms  even  as  an  abortive  structure 
may  thus  be  taken  to  indicate  the  transmitted  potentiality  of 
the  epiphyseal  complex  to  develop  a  visual  organ. 

The  theory  that  the  two  elements  in  the  epiphyseal  complex, 
namely,  the  pineal  and  parapineal  organs,  represent  a  pair  of 
parietal  eyes  similar  to  those  of  invertebrates,  has  little  to  recom- 
mend it.  The  hypothesis  of  Dendy86  that  the  ancestral  verte- 
brates were  possessed  of.  such  a  pair  of  visual  organs,  while 
interesting,  is  based  upon  too  few  facts  in  living  vertebrates  to 
justify  its  acceptance.  After  considering  the  several  theories 
concerning  the  relation  of  the  parietal  eye  to  the  pineal  body,  we 
have  come  to  the  conclusion  that  none  of  them  is  adequate  to 
explain  all  of  the  facts.  But  with  a  full  appreciation  of  the 
investigation  already  devoted  to  this  subject  we  desire  to  offer 
a  new  interpretation  which  to  us  seems  more  tenable.  Accord- 
rag  to  our  views,  there  is  no  direct  relation  between  the  parietal 
eye  and  the  pineal  body,  but  each  is  of  itself  an  adaptive  modifi- 
cation answering  the  demands  for,  or  representing  an  inherent 
impulse  toward,  the  development  of  a  parietal  eye,  on  the  one 
hand,  or  of  a  glandular  organ,  on  the  other.  In  other  words,  the 
epiphyseal  anlage  is  pluripotential  in  its  derivatives. 

5.  The  phylogenetic  significance  of  the  parietal  eye  with  reference 
to  vertebrates  and  invertebrates 

Much  has  been  written  concerning  the  significance  of  the 
parietal  eye  as  one  of  the  possible  indices  in  the  evolution  from 
invertebrates  to  vertebrates.  Although  little  evidence  bearing 
upon  this  point  has  been  presented  in  the  general  consideration 
of  this  work,  the  subject  seems  of  enough  interest  to  warrant  the 
inclusion  of  the  views  of  certain  investigators  who  have  devoted 
some  attention  to  this  matter. 


234  FREDERICK    TILNEY  AND    LUTHER   F.    WARREN 

Mathias  Duval98  in  1888  brought  to  a  conclusion  a  notable 
series  of  lectures  with  the  statement  that  the  history  of  the 
pineal  gland  has  played  an  important  role  in  the  study  of  homolo- 
gies  in  the  structure  of  the  vertebrates  and  invertebrates. 
He  further  states  that  the  situation  of  the  pineal  body  in  rela- 
tion to  the  nervous  system  of  vertebrates  and  in  comparison 
with  the  oesophageal  ring  in  invertebrates  gives  the  structure 
a  new  significance.  From  this  it  might  be  possible  to  determine 
one  of  the  clews  which  should  reveal  how  the  vertebrates  resulted 
from  the  successive  transformation  of  the  invertebrates. 

Several  years  prior  to  this  observation,  Ahlborn2  suggested 
that  the  parietal  organ  was  comparable  to  the  unpaired  eye  of 
amphioxus  and  tunicata,  while  Rabl-Ruckhard322  was  of  the 
opinion  that  an  homology  existed  between  the  pinal  organ  and 
the  parietal  eye  of  arthropoda.  Baudouin15  expressed  the  view 
that  of  the  proto-vertebrates,  larval  ascidians  possess  an  un- 
paired eye  which,  however,  disappears  in  the  adult.  This  organ 
is  situated  immediately  beneath  the  epidermis  and  consists  of 
a  retina,  a  lens,  and  a  pigment  layer.  It  is  derived  from  the 
cerebral  vesicle  and  supposed  to  be  the  vestige  of  a  transitory 
eye  which  previously  existed  in  adult  ascidians.  Indeed,  in 
pyrosomes  this  unpaired  eye  is  well  developed  in  the  adult, 
possessing  a  retina,  lens,  and  optic  nerve..  There  are  no  lateral 
eyes  in  these  invertebrates,  and  hence  the  unpaired  eye  must 
functionate  as  a  visual  organ.  In  tunicates  there  exists  both 
the  paired  and  unpaired  eyes.  In  amphioxus  there  is  a  pig- 
mentary patch  placed  above  a  dilation  of  the  brain,  but  one 
is  not  justified  in  considering  this  the  homologue  of  the  unpaired 
eye  in  tunicates. 

Peytoureau3083  held  the  opinion  that  the  pineal  eye  exists  in 
vertebrates  in  a  degenerated  state  only.  In  extant  forms  of 
the  tunicates  it  still  exists  as  a  functional  organ,  occupying  in 
these  animals  almost  exactly  the  same  position  and  having  the 
same  disposition  as  in  lizards  and  amphibia.  In  tunicates  there 
is  an  unpaired  eye  and  two  paired  eyes  which  he  believes  func- 
tionate simultaneously,  the  unpaired  eye  being  comparable  to 
the  parietal  eye  of  the  lizard  and  amphibia  not  only  because  of 


THE    PINEAL   BODY  235 

its  position,  but  also  because  of  its  anatomy  and  connections. 
He  is  of  the  opinion  that  the  unpaired  eye  is  more  ancient  than 
the  lateral  eyes.  This  is  the  more  probable  since  the  ancestors 
of  the  vertebrates  were  mon-ophthalmic,  examples  of  which  are 
to  be  found  in  the  pyrosomes  which  have  but  a  single  median 
eye.  Subsequently,  the  lateral  eyes  make  their  appearance  in 
tunicates  and  these  functionate  simultaneously  with  an  unpaired 
eye.  Peytoureau3083  gives  six  diagrams  showing  the  degenera- 
tive process  from  the  median  eye  of  pyrosomes  to  the  epiphysis 
in  the  higher  mammals,  as  follows:  1,  In  pyrosomes,  a  simple 
vesicle  with  a  lens;  2,  in  larval  urodela  there  is  a  vesicle  with 
nerve  connections  and  nerve  centers  but  no  lens;  3,  in  chamaeleon 
there  is  only  an  epithelial  vesicle  which  has  no  connections  or 
neural  characteristics;  4,  in  batrachians  the  organ  is  a  detached 
epithelial  cluster  having  no  connection  with  the  central  nervous 
system;  5,  in  cyclodus  the  organ  is  a  gland  attached  to  the  third 
ventricle  by  means  of  a  peduncle;  6,  in  mammals  and  birds  it  is 
connected  with  the  brain  by  a  solid  pedicle  but  presents  no  vesicle. 
Gaskell,146  in  his  summary  concerning  the  evidence  of  the 
organs  of  vision  and  their  bearing  upon  the  origin  of  vertebrates, 
writes  as  follows: 

The  most  important  discovery  of  recent  years  which  gives  a  direct 
clue  to  the  ancestry  of  the  vertebrates  is  undoubtedly  the  discovery 
that  the  pineal  gland  is  all  that  remains  of  a  pair  of  median  eyes  which 
must  have  been  functional  in  the  immediate  ancestor  of  the  vertebrate, 
seeing  how  perfect  one  of  them  still  is  in  Ammoccetes.  The  vertebrate 
ancestor,  then,  possessed  two  pairs  of  eyes,  one  pair  situated  laterally, 
the  other  median.  In  striking  confirmation  of  the  origin  of  the  verte- 
brate from  Palseostracans  it  is  universally  admitted  that  all  the  Euryp- 
terids  and  such-like  forms  resembled  Limulus  in  the  possession  of  a 
pair  of  median  eyes,  as  well  as  a  pair  of  lateral  eyes.  Moreover,  the 
ancient  mailed  fishes,  the  Ostracodermata,  which  are  the  earliest 
fishes  known,  are  all  said  to  show  the  presence  of  a  pair  of  median  eyes 
as  well  as  of  a  pair  of  lateral  eyes.  This  evidence  directly  suggests  that 
the  structure  of  both  the  median  and  lateral  vertebrate  eyes  ought  to 
be  very  similar  to  that  of  the  median  and  lateral  arthropod  eyes.  Such 
is,  indeed,  found  to  be  the  case. 

The  retina  of  the  simplest  form  of  eye  is  formed  from  a  group  of 
the  superficial  epidermal  cells,  and  the  rods  or  rhabdites  are  formed 
from  the  cuticular  covering  of  these  cells;  the  optic  nerve  passes  from 
these  cells  to  the  deeper-lying  brain.  This  kind  of  retina  may  be  called 


236  FREDERICK    TILNEY   AND    LUTHER    F.    WARREN 

a  simple  retina,  and  characterizes  the  eyes,  both  median  and  lateral, 
of  the  scorpion  group. 

In  other  cases  a  portion  of  the  optic  ganglion  remains  at  the  sur- 
face, when  the  brain  sinks  inwards,  in  close  contiguity  to  the  epidermal 
sense-cells  which  form  the  retina;  a  tract  of  fibres  connects  this  optic 
ganglion  with  the  under-lying  brain,  and  is  known  as  the  optic  nerve. 
Such  a  retina  may  be  called  a  compound  retina  and  characterizes  the 
lateral  eyes  of  both  crustaceans  and  vertebrates.  Also,  owing  to  the 
method  of  formation  of  the  retina  by  invagination,  the  cuticular  sur- 
face of  the  retinal  sense-cells,  from  which  the  rods  are  formed,  may  be 
directed  towards  the  source  of  light  or  away  from  it.  In  the  first  case 
the  retina  may  be  called  upright,  in  the  second  inverted. 

The  evidence  of  the  optic  apparatus  of  the  vertebrate  points  most 
remarkably  to  the  derivation  of  the  Vertebrata  from  the  Palseostraca. 

Gaskell,  in  this  argument,  seems  to  have  lost  sight  of  his 
well-known  contention  that  the  roof  of  the  brain  in  vertebrates 
is  to  be  considered  the  dorsal  wall  of  the  invertebrate  stomach. 
The  Stress  which  he  laid  upon  this  relation,  to  which  he  gave 
further  emphasis  by  calling  attention  to  the  glandular  appear- 
ance of  the  roof-plate  in  Ammocoetes,  does  not  coincide  well 
with  his  idea  that  the  pineal  body  is  primordially  a  portion  of  a 
neural  mechanism.  He,  of  course,  admits  that  the  pineal  eye  in 
vertebrates  must  be  considered  as  resulting  from  a  neural  in- 
vasion of  the  roof-plate,  yet  from  his  contention  this  roof-plate 
is  primitively  the  dorsal  wall  of  the  stomach,  and  neural  deriva- 
tives appearing  in  it  must  be  due  to  a  secondary  neural  invasion 
and,  therefore,  cannot  be  considered  primordial. 

In  a  word,  by  holding  the  pineal  eye  to  be  fundamentally 
neural  in  structure  he  did  injury  to  his  own  theory  concerning 
the  evolution  of  the  vertebrates. 

Patten,303  in  considering  the  significance  of  the  parietal  eye, 
gives  the  following  conclusions: 

The  parietal  eye  of  vertebrates  is  homologous  with  the  parietal  eye 
of  such  arthropods  as  Limulus,  scorpion,  spiders,  phyllopods,  cope- 
pods,  trilobites,  and  merostomes,  but  not  with  the  frontal  stemmata 
or  other  ocelli  of  insects. 

In  the  arthropods,  various  stages  in  the  evolution  of  a  cerebral  eye 
are  shown  in  detail,  from  functional  eyes  on  the  outer  margin  of  the 
cephalic  lobes,  to  a  median  group  of  ocelli  enclosed  within  a  tubular 
outgrowth  of  the  brain  roof. 


THE    PINEAL   BODY  237 

The  most  primitive  type  of  a  parietal  eye  is  seen  in  the  nauplii  of 
phyllopods  and  entomostraca,  where  the  eye  is  a  pear-shaped  sac,  open- 
ing by  a  median  pore  or  tube  on  the  outer  surface  of  the  head.  In  the 
higher  arachnids,  the  process  of  forming  an  embryonic  eye  vesicle 
merged  with  the  process  of  forming  a  cerebral  vesicle,  the  external 
opening  of  the  forebrain  vesicle  and  that  of  the  parietal  eye  tube,  form- 
ing a  common  opening  or  anterior  neuropore. 

The  parietal  eye  of  arthropods  is  an  important  visual  organ  until 
the  lateral  eyes,  which  represent  a  later  product,  are  fully  developed. 
It  may  then  diminish  in  size  and  activity,  but  it  rarely,  if  ever,  wholly 
disappears. 

During  the  revolution  of  vertebrates  from  arachnids,  there  was  a 
considerable  period  during  which  the  lateral  eyes  were  adjusting  them- 
selves to  their  new  position  inside  the  brain  chamber,  and  when  they 
were  in  functional  abeyance.  At  this  period,  ancestral  vertebrates 
were  mon-oculate,  that  is  they  were  dependent  solely  on  the  parietal 
eye,  which  had  come  to  them  from  their  arachnid  ancestors  as  an 
efficient  and  completely  formed  organ. 

When  the  lateral  eyes  again  became  functional,  the  parietal  eye 
began  to  decrease  in  size  and  effectiveness. 

The  parietal  eye  is  the  only  one  now  present  in  tunicates.  In  the 
oldest  ostracoderms,  like  Pteraspis,  Cyathaspis,  Palseaspis,  the  lateral 
eyes  are  absent,  or  at  least  do  not  reach  the  surface  of  the  head,  the 
only  functional  one  being  the  parietal  eye,  which  is  of  unusual  size. 

In  the  lampreys  we  see  the  same  conditions,  the  parietal  eye  being 
very  well  developed  in  the  larvae,  while  the  lateral  eyes  are  deeply 
buried  in  the  tissues  of  the  head,  and  useless.  During  the  transfor- 
mation, the  lateral  eyes  again  become  functional,  and  the  parietal 
begins  to  atrophy,  finally  losing  many  of  its  structural  details  and  its 
function,  although  still  retaining  very  nearly  its  original  form. 

All  the  theories  advanced  concerning  the  significance  of  the 
parietal  eye  as  an  index  to  the  process  of  evolution  from  the 
invertebrates  to  the  vertebrates  have  their  great  value  in  the 
suggestions  which  they  offer.  To  accept  any  of  them  without 
further  evidence  seems  unwise  at  the  present  time.  It  is  pos- 
sible to  conceive  of  the  median  eye  of  invertebrates  as  analogous 
to  the  parietal  eye  of  vertebrates.  It  is,  however,  a  long  step 
for  the  most  part  without  the  intervening  support  of  evidence  to 
maintain  that  these  structures  are  homologous.  In  fact  it 
seems  out  of  the  question  to  establish  any  such  basis  of  compari- 
son until  this  subject  of  homology  in  the  invertebrate  and  verte- 
brate brain  is  on  much  firmer  ground  than  it  is  to-day.  It  is 
evident  that  nothing  short  of  the  definite  establishment  of  an 


238  FREDERICK    TILNEY   AND    LUTHER    F.    WARREN 

invertebrate  pineal  region  of  the  brain  can  satisfy  the  require- 
ments in  this  field  of  homology.  Not  only  must  such  an  area  in 
its  general  outlines  be  recognized,  but  the  demonstration  must 
be  given  that  every  element  entering  into  it  has  its  homologue 
in  the  vertebrate  brain.  For  this  reason  it  seems  impossible  at 
present  to  accept  any  other  view  than  that  the  median  eye  in 
invertebrates  and  the  parietal  eye  of  vertebrates  are  analogous. 
The  supposition  that  they  are  homologues,  however  suggestive 
and  stimulating,  can  hardly  be  regarded,  at  present,  as  other 
than  speculative  morphology. 

8.  SUMMARY  AND  CONCLUSION 

I.  The  pineal  region  is  preponderatingly  glandiferous  in  its 
derivatives.  The  morphogenetic  impulse  imparted  by  such 
a  gland-forming  area  could  not  fail  to  have  a  profound  influence 
upon  one  of  its  constituents,  the  epiphysis. 

II.  a.  The  pineal  body  cannot  be  a  vestige  from  the  evidence 
based  upon  its  gross  morphology,  for  the  following  reasons:     , 

1.  The  phyletic  constancy  of  the  epiphysis  in  the  vertebrate 
phylum. 

2.  Its  variations  and  morphologic  specializations. 

3.  Its  relatively  greater  phyletic  constancy  with  reference  to 
other  structures  in  the  pineal  region. 

4.  The   gross   evidence   of   its   progressive   specialization   in 
ophidians,  birds,  and  mammals. 

5.  The   increase   in   the   epiphy so-cerebral   index,    from   the 
earliest  stages  to  the  latest  periods  of  life  in  man. 

6.  The  resistance  to  the  encroachment  of  a  prominent  neo- 
morph  in  the  mammalian  brain,  that  is,  the  corpus  callosum, 
which  has  produced  such  marked  alterations  in  the  other  con- 
stituents of  the  diencephalic  roof-plate. 

b.  The  pineal  gland  cannot  be  considered  a  vestige  in  the 
light  of  the  histological  evidence,  since  the  tendency  toward 
specialization  is  definitely  in  the  interest  of  glandular  formation 
in  ophidians,  chelonians,  birds,  and  mammals.  Ontogenetically, 
in  two  forms  at  least,  in  Felis  domestica  and  man,  the  develop- 


THE    PINEAL   BODY  239 

ment  of  the  pineal  body  follows  the  general  lines  of  glandular 
differentiation.  The  pineal  body  is,  therefore,  a  glandular 
structure  and  as  such,  is  necessary  in  some  way  to  metabolism. 

III.  The  histology  of  the  organ  gives  clear  evidence  that  the 
epiphyseal  complex  of  vertebrates  possesses  a  pluripotentiality 
whose  fundamental  inherent  tendency  is  in  the  interest  of  glandu- 
lar differentiation,  but  in  a  few  instances,  as  in  cyclostomes,. 
amphibia,  and  in  primitive  reptiles,  the  pineal  organ  may  become 
further   differentiated   in   the  interest   of  a  highly  specialized 
sensory  mechanism  which  has,  or  has  had,  visual  function.     As 
a  gland,  it  may  in  some  cases,  contribute  its  secretion  to  the 
cerebrospinal  fluid,  but  in  the  higher  vertebrates,  as  in  ophidians, 
chelonians,    birds,   and   mammals,   it   is   an   endocrinic   organ, 
contributing  the  products  of  its  secretion  to  the  blood  stream. 

IV.  a.  There  is  no  direct  relation  between  the  parietal  eye  and 
the  pineal  body,  but  each  is  of  itself  an  adaptive  modification 
answering  the  demands  for,  or  representing,  an  inherent  impulse 
toward  the  development  of  a  parietal  eye,  on  the  one  hand,  or  a 
glandular  organ,  on  the  other. 

6.  The  pineal  body  as  it  appears  in  mammals  cannot  be 
regarded  as  the  vestigial  or  metamorphosed  degenerated  or 
atrophic  residuum  of  the  parietal  eye  in  vertebrates. 

V.  The  phylogenetic  significance  of  the  parietal  eye  in  verte- 
brates as  the  homologue  of  the  median  eye  in  invertebrates 
should  be  accepted  with  much  reservation.     Until  such  time  as 
the  homology  between  the  vertebrate  pineal  region  and  some 
corresponding  area  of  the  invertebrate  brain  is  much  more  firmly 
established  than  at  present,  the  parietal  eye  as  an  index  in  the 
evolution  of  the  vertebrates  from  the  invertebrates  has  but  little 
value. 

The  authors  desire  to  acknowledge  their  great  indebtedness 
and  to  express  their  appreciation  to  Professor  George  S.  Hunt- 
ington  for  his  assistance  in  the  preparatine  of  this  monograph. 
They  also  wish  to  express  their  thanks  to  Professor  M.  Allen 
Starr  for  his  liberality  in  supplying  the  means  which  have  made 
publication  possible. 


240  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

• 

BIBLIOGRAPHY 

1  *  ACHUECARRO,   N.,  AND  SACRUTAN,  J.  M.     1912    Sobre  la  histologia  de 

la  glandula  pineal  humana.  Rev.  Clinica  de  Madrid,  8,  p.  336,  2  plates. 

2  AHLBORN,  F.     1883    Untersuchungen  iiber  das  Gehirn  der  Cyclostomen. 

Zeitschrift  f.  wiss.  Zool.,  Bd.  39,  S.  331. 

3  1884     Tiber    die    Bedeutung    der    Zirbeldriise     (Glandula    pinealis; 
Connarium.  Epiphysis  cerebri).     Ibidem,  Bd.  60. 

4  ANDRAL    1829    Precis  d'Anat.  Pathologique.     Paris. 

5  ANGLADE  AND  Ducos     1908    Note  preliminaire  sur  1'anatomie  et  la  physi- 

ologic de  la  glande  pineale.  Soc.  d'Anat.  et  de  Physiol.  de  Bordeaux. 
Process  verbal  officiel  de  la  seance  du  14  Decembre. 

6  1912    Sur  les  pedoncules  de  la  glande  pineale.     Jour,   de  Med.   de 
Bordeaux,  42>  p.  772. 

7  1912    Les  plaques  et  les  formations  lacunaires  dans  la  glande  pineale. 
Jour,  de  Med.  de  Bordeaux,  42,  p.  772. 

8  ARSAKY    Cited  by  Legros,  These  de  Paris,  1873. 

9  BAER    Uber    Entwickelungsgeschichte     der    Thiere.     Beobachtung    und 

Reflexion  I,  S.  130,  Konigsberg. 

10  BALFOUR,  F.  M.     1878    A  monograph  on  the  development  of  the  Elasmo- 

branch  fishes.     London,  p.  177. 

11  1881     Handbuch   der   vergleichenden   Embryologie.     Deutsch   v.    B. 
Vetter,  Jena. 

12  BALFOUR,  F.  M.,  AND  PARKER    1882    On  the  structure  and  development  of 

Lepidosteus  osseus.    Phil.  Trans.  Royal  Soc.,  vol.  1,  Pt.  11,  London 
(1878). 

13  BARALDI    1884    Due  parole  sulla  filogenia  del  corpo  pituitario  e  del  pineale. 

Pisa. 

14  BAUDELOT,  E.     1870    fitude  sur  Panatomie  comparee  de  1'enc^phale  des 

Poissons.     Mem.  de  la  Soc.  des  Sciences  Natur.  de  Strassbourg,  T.  6, 
2  Livr.,  p.  98. 

15  BAUDOUIN,  J.     1887    La  glande  pineale  et  le  troisieme  oeil  des  Vertebre's. 

Progres.  Medical,  No.  50-51. 

16  BAUHINUS    1616    Institutiones  anatomicae.     Francoforte. 

17  BEARD,  J.     1887    The  parietal  eye  in  fishes.     Nature,  vol.  36,  p.  246. 

18  1889    Morphological  studies,  No.  I.    The  parietal  eye  of  cyclostome 
fishes.     Quart.  Jour,  of  Micr.  Science,  vol.  29. 

19  BEAUREGARD,  F.     1881    Encephale  et  nerfs  craniens  du  Ceratodus  Forsteri. 

Jour,  de  1'Anat.  et  de  la  Physiologic. 

20  BECHTEREW,  WM.     1900    Les  voies  de  conduction  du  cerveau  et  de  la 

moelle.     Paris. 

21  BERANECK,  E.     1887    Uber  das  Parietalauge  der  Reptilien.     Jena.  Zeit- 

schrift, Bd.  21. 

22  1891     Sur  le  nerf  de  1'oeil  parietal.     Archives  des  Sciences  Physiques 
et  Naturelles,  Ser.  3,  T.  26. 

23  1892    Sur  le  nerf  parietal  et  la  morphologic  du  troisieme  oeil  des 
verte"bres.     Anat.  Anz.,  p.  674,  Oct.,  1892.     Centralb.  f.  die  Gesammte 
Wissensch.  Anatomic. 


*  This  reference  not  obtainable,  added  for  completeness. 


THE    PINEAL    BODY  241 

24  BERANECK,  E.     1893    Contribution  a  l'embroge"nie  de  la  glande  pine"ale  des 

Amphibiens.     Revue  suisse  de  Zoologie. 

25  1893    L'individualite,  de  1'oeil  parietal.     Reponse  a  M.  de  Klinchow- 
stroem.    Anat.  Anz.,  Bd.  6.   . 

26  1893    Anat.,  Anz.,  Bd.  8,  p.  669. 

27  BERNARD,  H.  M.     1897    An  attempt  to  deduce  the  vertebrate  eyes  from 

the  skin.     Quart.  Jour,  of  Micr.  Science,  vol.  39. 

28  BICHAT    1802    TraitS  d'Anat.  descriptive.     T.  3,  Paris. 

29  BIEHL    Citato  da  Poppi-L'ipofisi  cerebrale,  faringea  e  la  ghiandola  pineale 

in  patoligia. 

30  BIZZOZERO,   G.     1868    Sul  parenclrma  della  ghiandola  pineale.     R.   1st. 

Lomb.  di  Sc.  et  Lett.  Milano. 

31  1871     Beitrag  zur  Kenntnis  des  Baues  der  Zirbeldriise.     Vorlaufige 
Mitteilung.     Zentralb.  f.  Med.  Wissensch.,  No.  46,  Jahrg.  9. 

32  1871     Sulla  struttura  del  parenchima  della  ghiandola  pineale  umana. 
R.  1st.  Lomb.  di  Sc.  et  Lette.  Milano. 

33  1862-1879    Opera  Scient.     Milano,  1905,  1,  p.  175. 

34  BLANC,  H.     1900    Epiphysis  and  paraphysis  in  Salamandra  atra.     Arch. 

Sciences  Phys.  Nat.,  vol.  10,  p.  571. 

35  1900     Sur  le  development  de  1'epiphyse  et  de  la  paraphyse  chez  la 
Salamandra  atra.     Compt.  Rend.,  83.     Sess.  Helv.  Soc. 

36  BOJANUS,  L.  H.     1819-1821     Anatome  testudinis  europeae.     Vilnae. 

37  BORN,    G.     1889    Uber   das   Scheitelauge.     Jahrg.    d.    Schles.    Gessell.    f. 

Vaterlandische  Kultur,  Bd.  67. 

38  BORRICH  AND  HARDER     Cited  by  Legros.     These  de  Paris,  1873. 

39  BRAEM,    F.     1898    Epiphysis    und    Hypophysis    von    Rana.     Zeitschr.    f. 

Wiss.  Zool.,  Bd.  63. 

40  BRANDT,  E.  K.     1829     (Lacerta  agilis)  Medizinische  Zoologie,  Bd.  1,  p.  260. 

41  BUGNION,  E.     1897     Recherches  sur  le  developpement  de  Pepiphyse  et  de 

1'  organ  parietal  chez  les  Reptiles  (Iguana,  Lacerta,  Coluber).     Compt. 
Rend.  Trav.  80.  Sess.  Soc.  Helv.  Sc.  Nat.,  p.  56. 

42  BURCKHARDT,  R.     1890     Die  Zirbet  von  Ichthyophis  glutinosus  und  Pro- 

topterus  annectens.     Anat.  Anz.,  Jahrg.  6. 

43  1891     Untersuchungen  am  Hirn  und  Geruchsorgan  von  Triton  und 
Ichthyophis.     Zeitschr.  f.  Wiss.  Zool.,  Bd.  52. 

44  1892     Das  Zentralnervensystem  von  Protopterus  annectens.     Berlin. 

45  1893     Die  Homologien  des  Zwischenhirndaches  und  ihre  Bedeutung 
fur  die  Morphologic  des  Hirns  bei  niederen  Vertebraten.     Anat.  Anz., 
Jahrg.  9. 

46  1894     Die    Homologien    des   Zwischeithirndaches   bei    Reptilien    und 
Vogeln.  Anat.  Anz.,  Jahrg.  9,  no.  10 

47  1894    Der    Bauplan    des    Wirbeltiergehirns.     Morpholog.     Arbeiten 
von  G.  Schwalbe,  Bd.  4. 

48  BURDACH     1819-1826    Vom  Baue  und  Leben  des  Gehirns.  Leipzig. 

49  BIONDI,  C.     1912    Histologische  Beobachtungen  an  der  Zirbeldriise.  Zeit. 

f.  d.  Ges.  Neurol.  in  Psychiat.,  Bd.  9,  S.  43. 


MEMOIR   NO. 


242  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

50  CAMERON,  JOHN    1903    On  the  origin  of  the  pineal  body  as  an  amesial 

structure.     Anat.  Anz.,  Bd.  23,  S.  394. 

51  1903    Same  in  extenso.     Proc.  of  the  Roy.  Soc.  of  Edinburgh,  vol.  3, 
p.  340. 

52  1904     On  the  presence  and  significance  of  the  superior  commissure 
throughout  the  Vertebrata.     Jour,  of  Anat.  and  Physiol.,  vol.  38. 

53  CAJAL,    RAMON  Y.     1895    Apuntas   para  el   estudio   del  bulbo   raquideo 

cerebelo  y  origin  de  los  nervios  encefalicos.     Anales  de  la  sociedad 
Espanola  de  historia  natural. 

54  1904    Texture  del  sistema  nervioso  del  hombre  y  de  los  vertebrados. 
T.  2,  Madrid. 

55  CAMPER    Demonstrat.  Anat.  patholog.,  S.  12. 

56  CARRIERS,  J.     1885    Die  Sehorgane  der  Tiere,   vergleichend  anatomisch 

dargestellt.  Miinchen,  S.  205 

57  1890    Neuere   Untersuchungen   liber   das   Parietalorgan.    Biol.    Zen- 
tralbl.,  Bd.  9. 

58  CARRINGTON,  P.  G.     1890    On  the  pineal  eye  of  Lamna  cornubica  or  Por- 

beagle shark.     Proceed,  of  Roy.  Phy.  Soc.,  Sess.  90-91. 

59  CARUS,  C.  G.     1814    Versucheiner  Darstellung  des  Nervensystems.     Leip- 

zig, S.  149. 

60  CATTIE,  J.  T.     1882    Recherches  sur  la  glande  pineale  des  Plagiostomes, 

des  Ganoides  et  des  Teleostiens.     Arch,  de  Biol.,  T.  3. 

61  1883    tJber  das  Gewebe  der  Epiphyse  von  Plagiostomen,  Ganoiden 
und  Teleostiern.     Zur  Verteidigung.     Zeitschr.  f.  wissen.  Zool.,  Bd. 
39. 

62  CHARPY    1894    Encephale   in   Poirier.     Traite   d'Anat.    Humaine.     T.    3» 

Paris. 

63  CHAUSSIER    Cited  by  Legros.     These  de  Paris,  1873. 

64  CHAUVEAU,  A.     1885    Comparative  anatomy  of  the  domesticated  animals. 

Translated.     New  York,  p.  681. 

65  CIACCIO     1867    Intorno    allo    miriuta    fabbrica    della    pelle    della    Rana 

esculenta.     Palermo.     Cited  by  Leydig,  1891,  vol.  3,  p.  443. 

66  CIONINI,  A.     1885    Sulla  struttura  della  ghiandola  pineale.     Riv.  sperim. 

di  freniatria  a  di  Med.  Legale,  T.  11.  Reggio  Emilia,  Fasc.  1. 

67  1886    Sulla  struttura  della  ghiandola  pineale.     Ibidem  T.  12,  Fasc.  4. 

68  1888    La  ghiandola  pineale  e  il  terzo  occhio  dei  vertebrati.     Riv. 
sperim.  di  freniatria,  vol.  14.     Neurol.  Zentralb.,  1887,  No.  20. 

69  CLARKE     1860    Structure   of   the   pineal   gland.     Proceed,    of   the   Royal 

Soc.,  vol.  11. 

70  CONDORELLI-FRANCAVIGLIA     1895     L'encefalo   dell    'Helmaturus    dorsalis 

Gray.     Boll.  d.  Soc.  Romana  per  gli  studi  Zoologici.     T.  4. 

71  CONSTANTINI     1910     Intorno   ad   alcune   particolarita  di    struttura    della 

ghiandola  pineale.     Pathologica. 

72  CRUVEILHIER    Anatomie  pathologique. 

73  CRUVEILHIER  AND  SEE     1877    Traite  d'Anat.  Descriptive.     T.  3. 

74  CUTORE,  G.     1909    Di    una    particolare   formazione   prepineale    nel    Bos 

taurus  L.  Arch,  di  Anat.  e  di  Embriologia.     T.  3. 


THE    PINEAL   BODY  243 

75  CUTORE,  G.    1912    Alcune.notizie  sul  corpo  pineale  del  Macacus  sinicus 

L.  e  del  Cercopithecus  griseus  viridis  L.  Fol.  neuro-biol.,  T  6  No  4 
p.  267. 

76  1910    II  corpo  pineale  di  alcuni  mammiferi.     Arch.  Ital.  d.  Anat.  e 
di  Embriol.,  T.  9,  p.  402. 

77  CUVIER    1845    Lecons  d'Anatomie  Comparee,  T.  3,  p.  135. 

78  DA    FANO    1907    Osservasioni    sulla    fine    struttura    della    nevoroglia. 

Ricerche  fatte  nel  Laboratorio  di  Anatomia  normale  della  R.  Univer- 
sita  di  Roma,  etc.,  T.  12,  Fasc.  2-3,  Roma. 

79  DARKSCHEWITSCH,  L.  v.     1886    Anatomic  der  Glandula  pinealis.    Neurol. 

Zentralb.,  Bd.  5. 

80  1886    Einige  Bemerkungen  iiber  den  Faserverlauf  in  der  hinteren 
Commissur  des  Gehirns.     Neurol.  Zentralb.,  Bd.  5. 

81  DEAN,  BASHFORD     1888    The  pineal  fontanelle  of  Placodermata  and  cat- 

fish.    19.     New  York. 

82  1895    The  early  development  of  Amid.     Quart.  Jour.  Micr.  Science, 
vol.  38. 

83  1895    Fishes,  living  and  fossil.    New  York,  p.  53. 

84  DEBIERRE     1894    La  Moelle  e"piniere  et  PencSphale.     Paris. 

85  DEJERINE    1895    Anatomic  des  centres  nerveux.    Paris. 

86  DENDY,  A.     On  the  structure,  development  and  morphological  interpreta- 

tion of  the  pineal  organs  and  adjacent  parts  of  the  brain  in  the  Tuatara 
(Sphenodon  punctatum).  Philos.  Trans.  Soc.  London.,  Series  B, 
vol.  201. 

87  1899    On  the  development  of  the  parietal  eye  and  adjacent  organs  in 
Sphenodon  (Hatteria).     Quart.  Jour,  of  Micr.  Science,  vol.  42,  pt.  2, 
p.  111. 

88  DENDY  AND  NICOLLS    1910    On  the  occurrence  of  a  mesocoelic  recess  in 

the  human  brain,  and  its  relation  to  the  subcommissural  organ  of  the 
lower  vertebrates.  Anat.  Anz.,  Bd.  37. 

89  DESCARTES     1649    Les  Passions  de  TAme.     Art.  31  et  32.     Amsterdam. 

90  DEXTER,  F.     1902    The  development  of  the  paraphysis  in  the  common 

fowl.     Amer.  Jour.  Anat.,  vol.  2. 

91  DIEMERBROECK    1633    Anatome  corporis  humani.     Lugduni. 

92  DIMITROVA,  Z.     1901     Recherches  sur  la  structure  de  la  glande  pineale 

chez  quelques  mammiferes  la  Nevraxe,  T.  2,  Fasc.  3. 

93  DIONIS    1706    Anatomic  de  PHomme,  5  edit. 

94  DISDIER    1778    Esposit  exact,  ou  Tabl.  anat.  des   diff.    part   du   corps. 

humain.    Paris. 

95  DOHRN,   A.     1875    Der  Ursprung  der  Wirbeltiere  und  das  Prinzip  des 

Funktionswechsels.    Leipzig,  s.  87. 

96  1882    Studien  zur  Urgeschichte  des  Wirbeltierkorpers.  Mitteilungen 
aus  der  Zool.     Station  zu  Neapel.  Bd.  4. 

97  DUGES,  A.     1829    Memoire  sur  les  esp^ces  indigenes  du  genre  Lacerta. 

Annal.  des  Sciences  Naturelles.     T.  16,  p.  337. 

98  DUVAL,  M.     1888    Le  troisie"me  oeil  de  Vertebres.  Jour,  de  Micrographie,. 

Paris,  T.  12,  pp.  250,  273,  308,  336,  368,  401,  429,  459,  500,  523;  T.  13, 
pp.  16,  42,  76. 


244  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

99    DUVAL  AND  KALT    1889    Des  yeux  pineaux  multiples  chez  1'orvet.  Compt. 
Rend,  de  la  Soc.  de  Biol.  a  Paris.     T.  1,  No.  6. 

100  DUVERNEY    1761     Oeuvres  Anatomiques. 

101  ECKER,  A.     1857-1859    Icones  Physiologicae.  PI.  21,  fig.  7. 

102  1872    Gehirn  eines  Cebus  apella.     Arch.  f.  Anthropol.,  Bd.  5. 

103  EDINGER,  L.     1892    Untersuchungen  in  der  vergleichenden  Anatomic  des 

Gehirns.     II.  Das  Zwischenhirn  der  Selachier  und  der  Amphibien. 
Abhandlungen  der  Senchenberg.  Naturf.  Ges.  in  Frankfurt  a/M. 

104  1897    Lexioni  sulla  struttura  degli  organi  nervosi  centrali  deH'uomo 
e  degli  animali.  Trad.  Ital.  Milano. 

105  1900    Vorlesungen  uber  den  Bau  der  Nervosen  Zentralorgane.  Leipzig. 

106  1909    Bau  und  Verrichtungen  des  Nervensystems.  Leipzig. 

107  EDWARDS    (MILNE -EDWARDS)     1829    Recherches   zoologiques   pour   servir 

a  1'histoire  des  Lezards.     Annales  des  Sciences  Natur.,  T.  16,  p.  50. 

108  EHLERS,  E.     1878    Die  Epiphyse  am  Gehirn  der  Plagiostomen.     Zeit.  f. 

Wiss.  Zool.,  Bd.  30,  Supplement. 

109  D'ERCHIA,  F.     1896    Contributo  allo  studio  della  volta  del  cervello  inter- 

medio  e  della  regione  parafisaria  in  embrioni  di  pesci  e  mammiferi. 
Monit.  Zool.  Ital.,  Ann.  7. 

110  ELLENBERGER    1887    Vergleichende  Histologie  der  Haussaugethiere. 

111  ESTEVES  AND   BEATTi     1909    Klinische   und  Anatomische   Studien  eines 

Epithel.  der  Zirbeldriise.     Arch,  de  Pedagogia  de  la  Plata. 

112  EYCLESHYMER,   A.   C.     1892    Paraphysis  and  Epiphysis  in  Amblystoma. 

Anat.  Anz.,  Jahrb.  7. 

113  EYCLESHYMER  AND  DAVIS     1897    The  early  development  of  the  epiphysis 

and  paraphysis  in  Amia.     Jour,  of  Compt.  Neurol.,  vol.  2. 

114  FAIVRE,    E.     1855    Observations    sur    le    Conarium:     Comp.    Rend.    Soc. 

di  Biol.,  Paris. 

115  1857    Etude  sur  le  conarium  et  les  plexus  choroides  chez  Phomme  et 
les  animaux.     Annales  des  Sciences  Natur.,  Ser  4.,  T.  7. 

116  FAVARO     1903    Intorno  al  sacco  dorsale  del  pulvinar  pineale  neU'encefalo 

dei  Mammiferi.     Monitore  Zoologico  Ital.,  T.  14. 

117  1904    Di  un  organs  speciale  della  volta  diencefalica  in  Bos  taurus. 
Ibidem,  T.  15. 

118  1904    Le  fibre  nervose  prepineale  e  pineali  nell'encefalo  dei  mammiferi- 
Arch,  di  Anat.  e  di  Embriologia,  T.  3. 

119  FISH,  P.  A.     1895    The  central  nervous  system  of  Desmognathus  fusca. 

Jour.  Morph.,  vol.  10,  no.  1. 

120  FLATEAU-JACOBSOHN    1899    Handb.    u.    vergl.    Anat.    d.    Centralnerven- 

systems  der  Saugetaere.     Berlin. 

121  FLESCH,  MAX    1887    tlber  das  Scheitelauge  der  Wirbeltiere.     Mitteilun- 

gen  der  Naturf..  Ges.  in  Bern. 

122  1887    Struktur  des  zentralen  Nervensystems  des  Sympathikus  usw. 
In  Ellenberger:  Vergleichende  Histologie  der  Haussaugetiere.     Berlin 
S.  749. 

123  1888    tJber  die  Deutung  der  Zirbel  bei  den  Saugetieren.     Anat.  Anz., 
.       Bd.  3. 


THE    PINEAL   BODY  245 

124  FLECHSIG    1883    Plan  des  menschlichen  Gehirns.     Leipzig. 

125  FORSTER    1858    Virchow's  Arch.  f.  path.  Anat.,  13,  p.  271. 

126  FOSTER  AND  BALFOUR    1876    Grundziige  der  Entwicklungsgeschichte  der 

Tiere. 

127  FRANCOTTE,  P.     1887    Contribution  a  Petude  du  developpement  de  Pepi- 

physe  et  du  troisieme  oeil  des  reptiles.     Bull,   de  1'Acad.  Royal  de 
Belgique,  No.  12. 

128  1888    Recherches    sur   le    developpement   de    Pepiphyse.     Arch,    de 
Biol.,  T.  8,  p.  757. 

129  1894    Note  sur  Poeil  parietal  1'epiphyse,  la  paraphyse  et  les  plexus 
choroides  du  troisieme  ventricule.     Bull,  de  PAcad.  Roy.  de  Belgique, 
No.  1. 

130  1896    Contribution  a  Petude  de  Poeil  parietal  de  Pepiphyse  et  de  la 
paraphyse  -chez  les  Lacertilia.     Mem.  cour.  de  PAcad.  Roy.  de  Bel- 
gique, T.  55. 

131  FREY    1867    Handbuch  der  Histologie  und  Histochemie  des  Menschen. 

Leipzig,  S.  650. 

132  FULLIQUETTE,  G.     1886    Recherches  sur  le  cerveau  du  Protopterus  annec- 

tens.     Recueil  Zool.  Suisse. 

133  FUNKQUIST,  H.     1912    Zur  Morphogenie  und  Histogenese  des  Pinealorgans 

bei  den  Vogeln  und  Saugetieren.     Anat.  Anz.,  Jena,  Bd.  17,  s.  3. 

134  FURBINGER,      MAX     1902     Morphologische     Streitfragen.        Morpholog. 

7ahrbiicher,  Bd. .30,  S.  130. 

135  GAGE,   S.   P.     1893    The  brain  of  Diemyctylus  viridescens.     The  Wilder 

Quart.  Century  Book,  Ithaca,  N.  Y. 

136  1895    Comparative  morphology  of  the  brain  of  the  soft-shelled  turtle 
(Amida  mutica)  and  the  English  sparrow  (Passer  domesticus).     Pro- 
ceed, of  the  American  Microscop.  Soc.,  vol.  17. 

137  GALASESCU   AND   URECHIA    1910    Les   cellules   acidophiles  de   la   glande 

pineale.     Compt.  Rend.  Hebdom.  des  Seances  de  la  Societe  de  Biol., 
T.  68. 

138  GALEN    1576    De  usu  partium — L.  VIII  c.  3.     Galeni  omnia  quae  exstant 

opera.     T.  1,  5  ed.,  Venetiis. 

139  1679    De  Anat.  administ.  L.  IX  c.     3  Hippoc.  et  Galeni  opera.     T. 
4.     Lutetiae,  Parisorum. 

140  GALEOTTI,    G.     1896    Studie   morfologiche  e   citalogiche   della  volta  del 

diencefola  in  alcuni  vertebrati.     Rivista  di  Patol.  nervosa  e  mentale. 
T.  2. 

141  GALL    Cited  by  Legros.     These  de  Paris.     1873. 

142  GANSER    1882    Vergleichend-anatomrsche   Studien   iiber  das  Gehirn  des 

Maulwurfs.     Morph.  Jahrb.,  Bd.  5. 

143  GARMAN,   H.     1896     Some  notes  on  the  brain  and    pineal    structures    of 

Polyodon  folium.     Bull.  Illinois  State  Laborat.  of  Nat.  Hist.,  vol.  4. 

144  GARJANO,    C.     1909    Lo  sviluppo  dell'occhio  pineale.     Giornale  Interna- 

zion  delle  Science  Med.,  T.  31,  p.  505. 

145  GASKELL,  W.  H.     1890    On  the  origin  of  vertebrates  from  a  crustacean- 

like  ancestor.     Quart,  Jour,  of  Micro.  Science,  vol.  31. 

146  1908    The  origin  of  vertebrates.     London,  p.  117. 


246  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

147  GAUPP,  E.     1898    Zirbel,  Parietalorgan  und  Paraphysis.     Ergebnisse  der 

Anat,  und  Entwicklungsgeschichte  von  Merkel  und  Bonnet,  Bd.  7. 

148  1904    Lehre    vom    Integument   und    von    den    Sinnesorganen.     Das 
Stirnorgan.     Eckers  und  Wiedersheims  Anat.  des  Frosches.     Braun- 
schweig, S.  758. 

149  GERLACH,    F.     1917    Untersuchungen   an   der  Epiphysis  von   Pferd  und 

Rind.     Anat.  Anz.,  Bd.  50,  No.  3-4. 

150  GIANNELLI     1905    Contributo  allo   studio   comparative  delle  formazioni 

del  tetto  del  cervello  intermedio  in  base  a  ricerche  praticate  sul  loro 
sviluppo  in  embrioni  di  Rettjle  (Seps  chalcides)  e  Mammiferi  (Sus 
scropha  domesticus  e  Lepus  cuniculus).  Arch.  Ital.  di  Anat..  e  di 
Embriol.,  T.  4,  Firenze. 

151  GOETTE,  A.     1873    Kurze  Mitteilungen  aus  der  Entwicklungsgeschichte 

der  Unke.    Archiv.  f.  Mikr.  Anat,  Bd.  9. 

152  1875    Die  Entwicklungsgeschichte  der  Unke.     Leipzig. 

153  GORONQWITSCH,   N.     1888    Das  Gehirn  und  die  Cranialnerven  von  Aci- 

penser  ruthenus.     Morph.  Jahrbuch.,  Bd.  13. 

154  GOTTSCHE,  M.  C.     1835    Vergleichende  Anatomic  des  Gehirns  der  Graten- 

fische.    Muller's  Archiv.  f.  Anat.  u.  Phys.  Jahrb.,  p.  456. 

155  GRAAF,  H.  W.     de     1886    Zur  Anatomic  und  Entwicklung  der  Epiphyse 

bei  Amphibien  und  Reptilien.     Zoolog.  Anz.,  Jahrb.  9. 

156  GRANEL    1887    Le  glande  pineale,  Anatomic  comparee  et  fonctjons.     Gaz. 

Hebd.  des  Sciences  Nat  de  Montpellier,  p.  361. 

157  GRATIOLET    Anatomic    Comparee    du    Syste"me  nerveaux.     T.   2,    p.   73, 

(LeuretetGratiole't). 

158  GRAVENHEARST    1829    Reptilia  musei  Zoologici  Vratislaviensis.    Fasc.  1, 

Leipzig  (Tab.  7). 

159  GRIEB,    A.     1901     Contributione   allo    studio    delPorgano    parietale    del 

Podarcis  muralis.     Monitpre  Zoolog.  Italiano,  Ann.,  12,  No.  8. 

160  GUILLOT,   N.     1884    Exposition  anatomique  de  1'organization  du  centre 

nerveaux  dans  les  quatre  classes  d'animaux  verte"bres.     Paris. 

161  GUNZ     1753    De  lapillis  glandulae  pinealis  in  quinque  mente  alien  Lipsia. 

162  GUTZEIT    1896    Ein  Tera torn  der  Zirbeldriise.     Inag.  Dissert.,  Konigsberg. 

163  HACKEL    Archiv.  f.  Anat  und  Physiol.,  Bd.  16,  S.  259. 

164  HAGEMANN    1872    tJber  den   Bau   des   Conarium.     (Dissert.  Gottingen.) 

Arch.  f.  Anat.  und  Phys.,  S.  429. 

165  HALLER,  ALBRECHT    1768    De  Cerebro  avium  et  piscium.     Operum  ana* 

tomici  argumenti  minorum.     T.  3.     Lausannae. 

166  HALLER,    BELA     1898    Vom    Bau    des   Wirbeltiergehirns.     I.  Salmo    und 

Scyllium.     Morph.  Jahrb.,  Bd.  26. 

167  1900    II.  Emys.     Bd.  28. 

168  HANDRICK    1901    Zur  Kenntnis  des  Nervensystems  und  der  Leuchtorgane 

von  Argyropelecus  hemigymnus.     Bibliotjieca  Zool.,  Heft  32. 

169  A    HANITSCH,  P.     1888    On  the  pineal  eye  of  the  young  and  adult  of  Anguis 

fragilis.     Proc.  Liverpool  Biolog.  Soc.,  vol.  3,  p.  78,  1  plate. 
169  B    HEITZMANN    1896    Anat.  umana,  descrip.  e  Top.  Trad.  Ital. 
169  C    HECKSCHER,   W.     1890    Bidrag    til    kundskaben   om  Epiphysis  cerebri 

udviklings  historic.    Kjobenhavn. 


THE    PINEAL   BODY  247 

170  HARDER    Cited  by  Legros,  These  de  Paris,  1873. 

171  HENLE,    J.     1871     Nervenlehre.     In    Handbuch    der    Anatomic,    Braun- 

schweig.    Bd.  3,  Abt.  2,  S.  288. 

172  A         1879    Handbuch  der  Nervenlehre. 

172  B          1887    Handbuch  der  Systematischen  Anat.  des  Menschen.     Nerven- 

lehre. 

173  HENRICHS,    G.     1896    Untersuchungen  iiber  die   Anlage   des   Grosshirns 

beim  Hiihnchen.    Sitzungsber.  d.  Ges.  f .  Morphologic  und  Physiologic 
in  Munchen,  Bd.  12. 

174  HERD  MAN,  W.  A.     1886    Recent  discoveries  in  connection  with  the  pineal 

and  pituitary  body.     Proc.  Liverpool  Biolog.  Soc.,  vol.  1. 

175  HERTWIG,  O.     1908    Text-book  of  the  embryology  of  man  and  mammals. 

London,  p.  435. 

176  HERRICK,  C.  L.     1891    Topography  and  histology  of  the  brain  of  certain 

reptiles.    Jour.  Comp.  Neur.,  vol.  1,  3. 

177  1891     Contributions  to  the  morphology  of  the  brain  of  bony  fishes. 
Jour.  Comp.  Neur.,  vol.  1. 

178  HERRICK,  C.  J.     1891    Topography  and  histology  of  the  brain  of  certain 

ganoid  fishes.     Jour.  Comp.  Neur.,  vol.  1. 

179  HILL,  C.     1891    Development  of  the  epiphysis  in  Coregonus  albus.     Jour. 

Morph.,  vol.  3. 

180  1894    The  epiphysis  of  Teleosts  and  Amia.     Jour.  Morph.,  vol.  9. 

181  1900    Two  epiphyses  in  a  four-day  chick.     Bull,  of  the  Northwestern 
University  Med.  School.  Nov.,  1900. 

182  His,  W.     1868    Untersuchun^  n  iiber  die  ersten  Anlage  des  Wirbelthier- 

]eibes.    Leipzig. 

183  1892    Zur  allgemeinen  Morphologic  des  Gehirns.    Archiv.  f.  Anat. 
und  Physiol.,  Anat.  Abteilung. 

184  1893    Vorschlage  zur  Einteilung  des  Gehirns.    Archiv.  f.  Anat.  und 
Phys.,  Anat.  Abteilung. 

185  HOFFMANN,   C.  K.    1884    Zur  Ontogenie  der  Knochenfische.    Archiv.  f. 

Mikr.  Anat.,  Bd.  23. 

186  1886    Weitere    Untersuchungen    zur    Entwicklung     der    .Reptilien. 
Morph.  Jahrbuch.,  Bd.  11,  S.  192. 

187  1890    Epiphyse  und  Parieiialauge.     Bronns  Klassen  und  Ordnungen 
des  Tierreiches.    Bd.  6,  Abt.  3,  S.  1981.    Leipzig. 

188  HOLLARD,  H.     1837    Precis  d'Anat.     Comparee  en  tableau  de  1'organisa- 

tion  consistires  dans  Tensemble  de  la  se"rie  animale.     Paris,  p.  586. 

189  HOLT,  E.  W.  L.     1891     Observations  upon  the  development  of  the  Tele- 

ostean  brain,  with  especial  reference  to  that  of  Clupea  harengus. 
Zoolog.     Jahrbiicher,  Abt.  f.  Anat  und  Ontog.  d.  Tiere,  Bd.  4. 

190  HUMPHREY,  O.  D.    1894    On  the  brain  of  the  snapping  turtle  (Chelydra 

serpentina).     Jour.  Comp.  Neur.,  vol.  4. 

191  HUXLEY,  T.  H.     1876    On   Ceratodus  forsteri.     Proc.  Sc.  Meeting  Zool. 

Soc.  London. 

192  HYRTL    1889    Lehrb.  d.  Anat.,  9  Aufl.,  p.  777. 

193  JACKSON,  H.,  AND  CLARKE,  E.     1875     The  brain  and  cranial   nerves 

Echinorhynus  spinosus  with  notes  on  the  other  viscera.     Jour,  of 
Anat.  and  Phys.,  vol.  10. 


248  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

194  JOHNSTON,    J.    B.     1901     The   brain   of   Acipenser.     Zool.    Jahrb.,    Anat. 

Abt.,  Bd.  15. 

195  1902     The  brain  of  Petromyzon.     Jour.  Comp.  Neur.,  vol.  12. 

196  1909    The  morphology  of  the  forebrain  vesicle  in  Vertebrates.     Jour. 
Comp.  Neur.,  no.  19. 

197  JORDAN,  H.  E.     1911-1912    Histogenesis  of  pineal  body  of  sheep.     Amer. 

Jour.  Anat:,  vol.  12,  p.  249. 

198  1911     The  microscopic  anatomy  of  the  epiphys's  of  the  opossum. 
Anat.  Rec.,  Phil.,  vol.  5,  p.  325. 

199  1912    Results  of  recent  studies  of  the  mammalian  epiphysis  cerebri. 
Trans.  Am.  Micr.  Soc.,  31,  p.  231. 

200  JULIN,    C.     1887     De   la    signification   morphologique    de   Pepiphyse   des 

Vertebrcs.     Bull.  Scient,  du  Nord  de  la  France,  T.  10,  2  series. 

201  KARCHER,    J.    B.     1733    De    glanduli   pineali   lapides  ents.     Ref .    Index- 

Catalogue  of  the  Library  of  the  Surgeon-General's  Office.     U.  S.  A., 
vol.  13,  p.  378. 

202  KERR,    GRAHAM    1903    The    development  of   Lepidosiren   paradoxa.    Pt. 

III.     Quart.  Jour.  Micr.  Sc.,  vol.  46. 

203  KIDD,  L.  J.     1913    The  pineal  body;  a  review.     Review  of  Neurology  and 

Psychiatry,  vol  2,  p.  1. 

204  KINGSBURY,   B.    F.     1895    On   the  brain  of  Necturus  maculatus.     Jour. 

Comp.  Neur.,  vol.  5. 

205  1897    The  encephalic  evaginations  in  Ganoids.     Jour.  Comp.  Neur., 
vol.  7. 

206  KLINCKOWSTROEM,   A.   de     1892    Untersuchungen  iiber  den  Scheitelfleck 

bei  Embryonen  einiger  Schwimmvogel.     Zool.  Jahrb.,  Abt.  f.  Anat. 
u.  On  tog:,  Bd.  5. 

207  1893    Le  premier  developpement  de  1'oeil  parietal  Pepiphyse  et  de 
nerf  parfetal  chez  Iguana  tuberculata.     Anat.  Anz.,  Jahrb.  8. 

208  1893    Die  Zirbel  und  das  Foramen  parietale  bei  Callichthys  (asper 
und  littoralis).     Anat.  Anz.,  Jahrb.  8. 

209  1894    Beitrage  zur  Kenntnis  des  Parietalauges.  Zool.     Jahrb.,  Abt.  f. 
Anat.  u.  Ontog.  d.  Tiere. 

210  KOLLIKER,  A.  VON.     1850    Mikroskopische  Anatomic  des  Menschen.     Bd. 

2,  Leipzig. 

211  1879    Entwicklungsgeschichte  des  Menschen  und  der  hoheren  Tiere. 
Zweite  Auflage,  Leipzig. 

212  1887    Tiber  das  Zirbel  oder  Scheitelauge.    Sitzungsber  der  Wiirzburger 
phys.-med.  Geselsch.,  Miinchener  mediz.     Wochenschr.,  Bd.  34,  S  210. 

213  1896    Handbuch  der  Gewebelehre  des  Menschen.     Leipzig. 

214  KOLLMAN    1907    Handatlas   der   Entwicklungsgeschichte   der  Menschen. 

Zweiter  Teil. 

215  KORSCHELT,  E.     1886    Uber  die  Entdeckung  eines  dritten  Auges  bei  Wir- 

beltieren.    Kosmos,  Heft  3. 

216  KRABBE,  K.  H.     1915    Histologic  studies  of  the  pineal  gland.     Histologchi 

Andersogelsis  over  corpus  pineale.     Biblio  f .  Laeges,  Kibin  107,  p.  175. 

217  1911     Sur  la  Glande  Pineale  chez  PHomme.     Nouvell  Iconograph.  de 
la  Salpetriere.     T.  24,  p.  257. 


THE    PINEAL  BODY  249 

218  KRAUSE,  W.     1876    Allgemeine  und  mikroskopische  Anatomie.     Hanover. 

219  1868    Die  Anatomie  des  Kaninchens.     Leipzig. 

220  1884     Die  Anatomie  des  Kaninchens.     Leipzig. 

221  KRAUSHAAR,   R.     18S5     Entwicklung  der  Hypophysis  und  Epiphysis  bei 

Nagetieren.     Zeitschrift.  f.  Wiss.  Zool.,  Bd.  41. 

222  KUPFFER,  D.  VON    1887    Uber  die  Zirbeldriise  des  Gehirns.     Munch,  med. 

Wochenschrift,  Bd.  34,  S.  205. 

223  1893     Die  Entwicklung  des  Kopfes  von  Acipenser  sturio.     Studien 
zur  vergleichenden  Entwicklungsgeschichte  des  Kopfes  der  Kranio- 
ten.     Heft  1,  Miinchen. 

224  1894    Die  Entwicklung  des  Kopfes  von  Ammocoetes  planeri.     Idem., 
Heft  2. 

225  100    Zur  Kopfeixtwicklung  von  Bdellostoma.     Idem.,  Heft  4. 

226  1904     Die    Morphogenie    des    Zentralnervensystems.     In    Handbuch 
der  vergleichenden  u.  experimentellen  Entwicklungslehre  der  Wirbel-> 
tie  re.     Edited  by  O.  Hertwig.     Lief.  13-16. 

227  LEBERT    Anat.  patho.,  2,  p.  40. 

228  LEGGE,  F.     1896    Sullo  sviluppo  del  occhio  pineale  del  Gongylus  ocellatus 

Forsk.     Boll.  R.  Acad.  med.  Roma.  Anno  22. 

229  LEGROS     1873    Etude  sur  la  glande  pineale  et  ses  divers  etatspathologiques. 

These  de  Paris. 

230  LENDENFELD,  R.     1&88    Die  Leuchtorgane  der  Fische.     Biolog.  Zentralb., 

Bd.  7. 

231  LEYDIG,  F.     1853    Anatomisch-histologische  Untersuchungen  iiber  Fische 

und  Reptilien.     Berlin. 

232  1868    Traite  d'Histologie  Comp.  de  PHomme  et  des  Animaux,  p.  199. 

233  1868    Uber  Organe  eines  sechsten  Sinnes,  zugleich  ein  Beitrag  zur 
Kenntnis  des  Feineren  Baues  der  Haut  bei  Amphibien  und  Reptilien. 
Nova  Acta  Acad.     Leopold.  Carol.,  Bd.  34. 

234  1872    Die  in  Deutschland  lebenden  Arten  der  Saurier. 

235  1887     Das  Parietalorgan  der  Wirbeltjere.     Zool.  Anz.,  Jahrg.  10. 

236  1889    Das  Parietalorgan  der  Reptilien  und  Amphibien  kein  Sinnes- 
werkzeug.     Biolog.  Zentralb.,  Bd.  8,  S.  706. 

237  1890     Das    Parr  talorgan.     Zweite    vorlaufige     Mitteilung,     Biolog. 
Zentralb.,  Bd.  10,  S.  278. 

238  1891     Das   Parietalorgan   der  Amphibien   und   Reptilien.    Abhand- 

ungen  der  Senckenbg.  Gesellsch.,  Frankfurt  a/M.,  Bd.  16. 

239  1896    Zur  Kenntnis  der  Zirbel  und  Parietalorgane.    Abhandlungen 
der  Senckenbg.  Naturf .  Ges.  Frankfurt  a/M.,  Bd.  16. 

240  1897    Zirbe    und  Jacobsonsche  Organe  einiger  Reptilien.     Archiv.  f. 
Mikr.  Anat.,  Bd.  50. 

241  LESSONA,    M.     1880    Sulla   ghiandola   frontale    degli   anfibi   anuri.    Atti 

della  Reale  Acad.  d.  Science  di  Torino.     T.  15. 

242  LIEBERKUHN,  N.     1871    Uber  die  Zirbeldriise.     Sitzungsber,  d.  Gesellsch. 

zur  Beforderung  d.  Naturwiss.  zu  Marburg.     No.  4,  June  29. 

243  LOOT,  W.  A.     1893    The  derivation  of  the  pineal  eye.    Anat.  Anz.,  Bd.  9, 

S.  169. 


250  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

244  Locr,  W.  A.     1894    The  optic  vesicles  of  Elasmobranchs  and  their  serial 

relation  to  other  structures  on  the  cephalic  plate.     Jour  Morph., 
vol.  9. 

245  1894    The  midbrain  and  the  accessory  optic  vesicles.     Anat.  Anz., 
Jahrb.  9. 

246  1894    Metameric  segmentation  in  the  medullary  folds  and  embryonic 
rim.     Anat.  Anz.,  Jahr.  9. 

247  1895    Contribution  to  the  structure  and  development  of  the  verte- 
brate head.     Jour.  Morph.,  vol.  11. 

248  LONGET,  F.  A.     1847    Anatomic  und  Physiologic  des  Nervensystems  d. 

Menschen  und  der  Wirbeltiere.     Bd.  1,  Leipzig. 

249  LORD,  J.  R.     1899    The  pineal  gland;  its  normal  structure,  some  general 

remarks  on  its  pathology;  a  case  of  syphilitic  enlargement.     Transact, 
of  the  Pathological  Society  of  London,  vol  50,  p.  18. 

250  LOTHEISSEN    1894    tlber  die  Stria  medullaris  Thalami  optici  und  ihre 

Verbindungen.     Vergleichend  =  Anat.   Studie,   Anatomische  Hefte. 

251  LUDWIG    Scripty  Neurol.  Memories,  T.  4. 

252  LUSCHKA    1867    Die  Anatomic  des  Menschen.     Tubingen. 

253  LUYS     1865    Recherches  sur  le  systeme  nerveux  cerebrospinale.     Paris. 

254  MclNTosH  AND  PRINCE    1891     Development  and  life  histories  of  food  and 

other  fishes.     Transact.  R.  Soc.  Edinburgh,  vol.  35. 

255  McKAY,   E.   J.     1888    Development  and  structure  of  the  pineal  eye  in 

Hinulia  and  Grammatophora.     Proceed,  of  the  Linnean  Society  of 
New  South  Wales,  2  ser.,  vol.  3,  p.  332. 

256  MAJENDIE     1828    Memoir  physiologique   experimentale   et  pathologique. 

T.  7,  p.  211. 

257  1795    Encefalotomia  di  Alcuni  Quadrupi.     T.  4,  p.  31. 

258  MALACARNE    Cited  by  Legros,  These  de  Paris,  1873. 

259  MARBURG,  O.     1908-1909    Zur  Kenntnis  der  normalen  und  pathlogischen 

Histologie  der  Zirbeldriise  die  Adipositas'  cerebralis.     Arbeiten  a.d. 
Neurol.  Institut.  a.  d.  Wien.  Univ.  Leipzig  und  Vienna,  Bd.,  17,  S.  217. 

260  1912    Die   Klinik   der  Zirbeldriisen   Krankungen.     Ergeb.    Med.    u. 
Kinderh.,  Bd.  10,  S.  146. 

1908    Adipositas  cerebralis.     Wien.  Med.  Wchnschr.,  58,  2617. 

261  MARSHALL    1861     On  the  brain  of  a  young  chimpanzee.     Nat.  Hist.  Review. 

262  1893    Vertebrate  embryology.     London. 

263  MAWAS,   J.     1910    Note   sur  la  structure  et  la  signification  glandulaire 

probable  des  cellules  neuroglique  du  Systeme  nerveus  central  des 
Vertebres  Seance  et  Memoir  de  la  Soc.  de  Biol.  vol.  69,  p.  45. 

264  MAYER,  F.     1897    Das  ZentralnervensystemvonAmmocoetes.     I.     Vorder 

Zwischen  und  Mittelhirn.     Anat.  Anz.,  Jahrb.  13. 

265  1864    tTber  den  Bau  des  Gehirns  der  Fische.     Nova  Acta  Akad.     Leo- 
pold, Bd.  30. 

266  MECKEL,  J.  F.     1815    Versuch  einer  Entwicklungsgeschichte  der  Zentral- 

teile  des  Nervensystems  in  den  Saugetiereh.     Deutsch.  Arch.  f.  Phys., 
Bd.  1,  S.  644. 

267  1765    1795    Observationes    anatomicae    de    glandula    pineali,    septo 
lucido,   et  origine  paris  septimi  nervorum  cerebri.     Scrip.   Neurol. 
Memor.  Select.  Lipsiae.  9-10. 


THE    PINEAL  BODY  251 

268  MEHNERT,    E.     1898    Biomechanik.     Erschlossen    aus    dem    Prinzip    der 

Organogenese.     Fischer. 

269  MELCHERS,    F.     1899    tlber  rudimentare   Hirnanhangsgebilda  bei   Gecko 

(Epipara  und  Hypophyse).     Zeit^chr.  f.  Wiss.  Zoll.,  Bd.  67. 

270  MESTREZAT,    W.     1912    Le   liquide   cephalo-rachidien,   normal  et  patho- 

logique.     Paris. 

271  MEYNERT,  T.     1877    Vom  Gehirn  der  Saugetiere.    Strickers  Handb.  der 

Lehre  von  Geweben,  Bd.  2,  S.  743. 

272  MICLTJCHO  MACLAY,  N.     VON    1870    Beitrage  zur  vergleichenden  Neurol- 

ogic der  Wirbeltiere.     Leipzig. 

273  MIDDLEMAAS     1895    A  heavy  brain.     The  Lancet,  p.  1432. 

274  MIHALKOVICZ,  V.     1874    Entwicklung  der  Zirbeldriise.     Zentralb.  f.  med. 

Wiss.,  No.  17. 

275  1877    Entwicklungsgeschichte  des  Gehirns.     Leipzig,  S.  94. 

276  MINGAZZINI     1889    Organi  nervosi.     Roma. 

277  MINOT,  C.  S.     1901     On  the  morphology  of  the  pineal  region,  based  upon 

its  development  in  Acanthias.     Amer.  Jour.  Anat.,  vol.  1. 

278  MOLLER,  J.  VON    1890    Einiges  liber  die  Zirbeldriise  des  Chimpanse.     Ver- 

handl.  d.  naturf.  Gesellsch.  in  Basel,  S.  755. 

279  1890    On  the  anatomy  of  t^he  chimpanzee  brain.    Archiv  f.  Anthro- 
polgie,  Bd.  17. 

280  MULLER,  JOHANNAS    1838    Vergleichende  Neurologic  der  Myxinoiden.  Ver- 

handl.  der  Akad.  d.  Wissenschaften  in  Berlin. 

281  NAGEOTTE,  J.     1910    Phenomenes  de  Secretion  dons  le  protoplasma  des 

cellules  nevroglique  de  la  substance  grise.  Seances  et  Memoir  de  la 
Soc.  Biol.,  T.  68,  p.  1068. 

282  NEUMEYER,  L.     1899    Studie  zur  Entwicklungsgeschichte  des  Gehirns  der 

Saugetiere.     Festschrift  zum  70.     Geburtstag  von  Carl  von  Kupffer. 
283A  NICOLAS,  M.     1891    Sur  le  troisieme  oeil  der  Verfie'bres. 
283B  1900    Note  sur  la  presence  des  fibres  muscularies  striees  dans  la  glande 

pineale  de  quelques  mammiferes.     Comp.  Rend,  de  la  Soc.  de  Biol., 

Paris,  T.  2,  p.  876. 

284  OBERSTEINER    1893    Anatomic  des  centres  nerveux.     Trad,  franc. 

285  ORIBASIUS     1554    Synopseos  ad  Eustathium  filium.     Libri  IX,  quibus  tota 

Medicina  in  compendium  redacta  continetur.     I.  B.  Rosario  inter- 
prete.     Venetiis. 

286  ORR    1899    Note  on  the  developmen't  of  Amphibians,  chiefly  concerning 

tjie  central  nervous  system.     Quart.  Jour,  of  Micr.  Science,  vol.  29. 

287  OSBORN,   H.   F.     1883    Preliminary  observation  upon  the  brain  of  Am- 

phiuma.     Proceed.  Philadelphia  Acad.  Nat.  Sc. 

288  1884    Preliminary  observations  upon  the  brain  of  Menopoma  and 
Rana.     Idem. 

289  1889    Contributions  to  the  internal  structure  of  the  Amphibian  brain. 
Jour.  Morph.,  vol.  2,  no.  1. 

290  1887    A  pineal  eye  in  the  Mesozoic  Mammalia.     Science,  N.  Y.,  p.  92. 

291  OSTROTTMOFF,  F.  VON    1887    Zur  Frage  uber  das  dritte  auge  der  Wirbeltiere 

96.     Beilage  zu  den  Protokollen  der  naturf.  Ges.  an  der  kais.     Uni- 
sitat  zu  Kasan,  1-13. 


252  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

292  OWEN    1837    Structure  du  cerveau  des  Marsupiaux.     Annales  des  Sciences 

Naturelles,  2  series,  T.  8,  Zoologie,  Paris. 

293  1881     On  the  homology  of  the  conario-hypophyseal  tract  or  the  so- 
called  pineal  and  pituitary  glands.     Linnean  Soc\  Jour.  Zool.,  p.  131. 

294  1866    Anatomy  of  the  Vertebrates,  vol.  1,  p.  280,  London. 

295  OWSIANNIKOW,  P.     1888    Uber  das  dritte  auge  bei  Petromyzon  fluviatilis, 

nebst  einigen  Bemerkungen  liber  dasselbe  Organ  bei  anderen  Tieren. 
Memoires  de  1'Acad.  Imper.  de  St.  Petersbourg,  Ser.  7,  T.  36. 

296  1890    tiber  das  Parietalauge  von  Petromyzon.     Travaux  de  la  Soc. 
des  Naturalistes  de  St.  Petersbourg.  Sect.  Zool.,  T.  15,  Pt.  1. 

297  1890    tibersicht  der  Untersuchungen  iiber  das  Parietalauge  bei  Am- 
phibien,  Reptilian  und  Fischen.     Revue  des  sc.  naturelles  de  la  soc. 
des  naturalistes  de  St.  Petersbourg,  Annee  2,  No.  2. 

298  PAPPENHEIMER    1910    Uber  Geschwiilste  des  Corpus  pineale.     Virchow's 

Archiv  f.  path.  Anat.,  p.  122. 

299  PARDI     1909    Per  la  storia  e  la  migliore  conoscenza  dei  clasmatociti  di 

Ranvier — Atti  d.  societa  Toscana  di  Scienze  Naturali  Memorie,  T.  25. 

300  PARISINI     Cited  by  Cutore  in  il  Corpo  pineale  di  alcuni  Mammiferi.     Arch. 

Ital.  di  Anat.  e.  di  Embriol.,  T.  9,  p.  402,  1910. 

301  PARKER,  JEFPERY    1892    Observations  on  the  anatomy  and  development 

of  Apteryx.     Phil.  Transact,  of  the  Roy.  Soc.  of  London  for  the  year 
1891,  vol.  182. 

302  PARKER,  J.,  AND  HASWELL,  W.  A.     1897    A  text-book  of  zoology,  vol.  2, 

London. 

303  PATTEN,   WILLIAM    1890    On  the  origin  of  vertebrates  from  Arachnids. 

Quart.  Jour,  of  Micr.  Science,  vol.  31,  p.  340. 

304  1894    On  the  morphology  and  physiology  of  the  brain  and  sense  organs 
of  Limulus.     Quart.  Jour,  of  Micr.  Science,  vol.  35,  p.  76. 

305  PAWLOWSKY     1874    tiber  dan  Faserverlauf  in  der  hinteren  Gehirncom- 

missur.     Zeitschr.  f.  wiss.  Zool.,  Bd.  24. 

306  PERRAULT    Cited  by  Legros,  These  de  Paris,  1873. 

307  PETTITT  AND  GERARD     1902-03    Sur  la  function  secretoire  et  la  morphologic 

des  plexus  Choroides.     Arch.  d'Anat.  Micros.,  5. 
308A  PEYTOUREAU,  S.  A.     1886    La  glande  pineale  et  le  troisieme  oeil  des  Ver- 

tebres.     Bordeaux,  1887.     These  de  Bordeaux,  No.  95,  p.  68,  142  fig. 
308B          1889    La  glande  pineale  et  la  troisieme  oeil  des  Vertebres.     These  de 

Paris. 

309  POLEJAEFF,   N.    -1891     tiber  das  Scheitelauge  der  Wirbeltiere  in  seinem 

Verhaltnis  zu  den  Seitenaugen.     Revue  Scientifique  de  la  Societe  des 
Naturalistes  de  St.  Petersbourg,  No.  5,  p.  178. 

310  POLVANI,  F.     1913     Studio  anatomic o  della  glandula  pineale  umana  Ras- 

s  gua  di  studio  psiclrat.     Siena,  T.  3,  p.  3. 

311  PRENANT,   A.     1893    Sur  1'oeil   parietal    accessoire.     Anat.   Anz.,    Jahrb. 

9,  No.  4. 

312  1895    Les  yeux  parietaux  accessoires  d'Anguis  fragilis  sous  le  rapport 
i             de  leur  situation,  de  leur  nombre  et  de  leur  frequence.     Bibliographie 

anatcmique    T.  1. 


THE    PINEAL   BODY  253 

313  PRENANT,  A.     1896    Elements  d'embryologie  de  1'homme  et  des  vertebres. 

Livre  deuxieme,  Paris,  p.  566. 

314  1896    L'appareil  pineal  de  Scincus  officianalis  et  de  Agama  bibroni. 
Bull,  de  la  soc.  des  sciences  de  Nancy. 

315  PRENANT  AND  BOTJIN    1911     Traite  d'Histologie.     T.  2,  Paris. 

316  RABL-RUCKHARD,  H.    1878    Das  Zentralnervensystem  des  Alligator.     Zeit- 

schrift  f.  wiss.  Zool.,  Bd.  30. 

317  1880    Das  gegenseitige  Verhaltnis  der  Chorda.     Hypophysis  und  des 
mittleren  Schadelbalkens  bei  Haifischembryonen.    Morpholog.  Jahrb., 
Bd.  6. 

318  1882    Zur  Deutung  und  Entftvicklung  des  Gehirns  der  Knochenfische. 
Archiv.  f.  Anat.  und  Physiol.,  Anat.  Abteilung. 

319  1883     Das  Grosshirn  der  Knochenfische  und  seine  Anhangsgebilde. 
Archiv.  f.  Anat.  und  Physiol.,  Anat.  Abteilung. 

320  1884    Das  Gehirn  der  Knochenfische.     Biolog.  Zentralblatt,  Bd.  4, 
Deutsch  med.  Wochenschr.,  No.  33. 

321  1884    Weiteres  zur  Deutung  des  Gehirns  der  Knochenfische.     Biolog. 
Zentralblatt,  Bd.  3. 

322  1886    Zur  Deutung  der  Zirbeldrlise    (Epiphyse).     Zoologischer  An- 
zeiger,  Jahrb.  9. 

323  1894    Einiges  iiber  das  Gehirn   der  Riesenschlange.     Zeitschrift  f. 
wiss.  Zool.,  Bd.  54. 

324  REAL  COLUMBI     1559     De  re  Anatomica.     Venetiis. 

325  REGULEAS     1845    Lezioni  di  Anatomica  Umana:    T.  3,  pt.  2,  Catania. 

326  REICHERT,  K.  B.     1859-1861     Der  Bau  des  menschlichen  Gehirns.    2  Abt. 

Leipzig. 

327  REINHOLD,  H.     1886    Inaug.  Dissert.     Leipzig. 

328  REISSNER     1864    Der  Bau  des  Zentralnervensystems  der  ungeschwanzten 

Batrachier.     Dorpat, 

329  1851     De  Auris  internae  formatione.     Dorpat. 

330  REMAK    Observat.  Anat.  de  System  Nervor.  Structur.    S.  26. 

331A  RETZIUS,  A.  1822  Bidrag  til  Ader  og  Nerfsystemets  anatomic  hos  Myxine 
glutinosa.  Kong".  Veten,  akad.  Handlingar,  Stockholm. 

331B  RETZIUS,  G.  1895  tlber  den  Bau  des  sogen.  Parietalauges  von  Ammo- 
coetes.  Biolog.  Untersuchungen,  N.  F.,  Bd.  7. 

332  RITTER,  W.  E.     1891     The  parietal  eye  in  some  lizards  from  the  western 

United  States.     Bull,  of  the  Museum  of  Comp.  Zool.,  vol.  20. 

333  1894    On  the  presence  of  a  parapineal  organ  in  Phrynosoma  coronata. 
Anat.  Anzeiger,  Jahrb.  9. 

334  ROBIN    Cited  by  Legros,  These  de  Paris,  1873. 

335  ROLANDO     Jour.  Majendie,  vol.  3. 

336  ROMITI     1882    Lo   sviluppo  del  conario.     Atti  d.   Soc.   Toscanda  di  Sc. 

Naturali  Prox.  verbali,  T.  3. 

337  ROMITI  AND  PARDI     1906     Clasmatoeytes  et  Mastzellen.     XV  Congress 

in  International  de  Medicine.     Section  1  (Anatomie),  Lisbonne. 

338  Anatomia  deH'umana.     Milano. 

339  RUYSCH     Thesaurus  anatomicus  quintus.     Tab.  3,  sec.  18. 


254  FREDERICK   TILNEY   AND    LUTHER   F.    WARREN 

340  SAINT  REMY,  G.     1897    Notes  teratologiques.     I.  Ebauches  epiphysaires 

et  paraphysaires  paires  chez  un  embryon  de  poulet  monstrueux.  Bib- 
liographic anatomique,  T.  5. 

341  SALENSKY,  W.     1881    Recherches  sur  le  developpement  du  sterlet  (Aci- 

penser  ruthenus).  Archives  de  Biologic,  Bd.  2  und  3.  (Arbeiten  der 
naturforschenden  Gesellschaft  an  der  kaiserlichen  Universitat  zu 
Kasan,  1879.) 

342  1894    Morp.iolo^'sche  Studien  an  Tunicaten.     I.  Uber  das  Nerven- 
sy^teiu  der  Larve  und  Embryonen  von  Distaplia  magnilarva.     Mor- 
phol.  Jahrb.,  Bd.  20,  S.  69. 

343  SANDERS,  A.     1889    Contribution  to  the  anatomy  of  the  central  nervous 

system  in  Ceretodus  forsteri.  The  Annals  and  Mag.  of  Natur.  His- 
tory, London. 

344  SAPPEY    1887    Traite  d'Anatomie  descriptive,  T.  3. 

345  SARTESCHI,  U.     1910    Ricerche  istologiche  sulla  glandula  pineale.     Folia 

neuro-biologica,  p.  675. 

346  SCHAUINSLAND,    H.     1899    Beitrage    zur   Biologic    und    Entwicklung   der 

Hatlberia,  nebst  Bemerkungen  Tiber  die  Entwicklung  der  Sauropsiden. 

Anat.  Anzeiger,  Jahrb.  15. 
347A  1903    Beitrage  zur  Entwicklungsgeschichte  und  Anatomic  der  Wirbel- 

tiere.     I-III.     Bibliotheca  zoologica,    Stuttgart. 
347B       SCHMIDT    1862    Beitrage  zur  Entwicklung  des  Gehirns.     Zeitsch.  wiss. 

Zool.,  Bd.  11. 
347C       SCHLEMM  UND  D'Ai/roN    1838    Uber  das  Nervensystem  dor  Petromy- 

zonten.     Miiller's  Archiv. 

348  SCHWALBE,  G.     1881     Lehrbiich  der  Neurologic.     (Hoffmann's  Handbuch 

der  anatomic  des  Menschen.     2  Aufl.,  Bd.  2,  Abt.  2.) 

349  SCOTT,  E.  B.     1881     Beitrage  zur  Entwicklungsgeschichte  von  Petromyzon. 

Morphol.  Jahrbuch,  Bd.  7. 

350  1888    The  embryology  of  Petromyzon.     Jour.  Morph.,  vol.  1. 

351  SEIGNEUR,  P.     1912    Etude  critique  sur  la  glande  pineale  normale  et  patho- 

logique.     These  de  Paris,  No.  375. 

352  SELENKA,  E.     1890    Das  Stirnorgan  der  Wirbeltiere.     Biolog.  Zentralbl., 

Bd.  10. 

353  SERRES     1824--1828    Anatomic  comparee  du  cerveau  dans  les  quartre  classes 

des  animaux  vertebres.     Paris. 

354  SHIPLEY,  A.  E.     1887    On  some  points  in  the  development  of  Petromyzon 

fluviatilis.     Quart.  Jour,  of  Micr.  Science,  vol.  27. 

355  SIEBOLD  ANDSTANNIUS     1854    Handbuch  der  Zootomie.  Bd.  2.  Die  Wirbel- 

tiere.    2  Aufl.,  Berlin. 

356  1846    Lehrbuch  der  Vergleichende  Anat.,  2,  p.  59. 

357  SMITH,  G.  ELLIOT    1897    On  the  morphology  of  the  cerebral  commissures, 

etc.     Trans.  Linnean  Soc.  London,  8,  2  series.     Zool.,  p.  455. 

358  SOEMMERING    1785    De  Capillis  vel  prope,  vel  untra  glandulam  pinealem 

sitis  Magonza. 

359  1785    Scriptores  neurolog.  mimores  selectit,  T.  3. 

360  1798    De  corpor.  humani  fabrica,  T.  4. 


THE    PINEAL   BODY  255 

361  SORENSEN,  A.  D.     1893    The  pineal  and  parietal  organ  in  Phrynosoma 

coronata.    Jour.  Comp.  Neur.,  vol.  3. 

362  1893    The  roof  of  the  Diencephalon.     Jour.  Comp.  Neur.,  vol.  3. 

363  1894    Comparative  study  of  the   epiphysis  and   roof   of    the   Dien- 
cephalon.    Jour.  Comp.  Neur.,  vol.  4. 

364  SSOBOLEW,  L.  W.     1907    Zur  Lehre  von  Paraphysis  und  Epiphysis  bei 

Schlangen.     Arch.  f.  Micro.  Anat.,  Bd.  70,  S.  318. 

365  SOURY    1899    System  neryeux  central.     Paris. 

366  SPENCER,  E.  BALDWIN.  1886    The  parietal  eye  of  Hatteria.    Nature,  vol. 

34. 

367  1886    Preliminary  communication  on  the  structure  and  presence  in 
Sphenodon  and  other  lizards  of  the  median  eye,  described  by  Von 
Graaf  in  Anguis  fragilis   (communicated  by  Prof.  H.   N.  Moseley). 
Proceedings  of  the  Roy.  Soc.  of  London,  June  10. 

368  1886    On  the  presence  and  structure  of  the  pineal  eye  in  Lacertilia. 
Quart.  Jour,  of  Micr.  Science,  vol.  27,  pp.  165-238. 

369  1890    The  pineal  eye  of  Mordacia  mordax.     Roy.  Soc.  of  Victoria. 

370  SPERINO   AND   BALLI     1909    L'encefalo  del  Dasyprocta  aguti.    Memorie 

della  r.  Acad.  di.  Scienze.  Lettere  ed  Arti  in  Modena.  Serie  3,  T.  10, 
Sezione  Scienze,  Modena. 

371  SPRONCK    1887    De  epiphysis  cerebri  als  rudiment  van  een  derde  of  parietal 

organ.     Neederl.  Weekbl.,  No.  7. 

372  STADERINI     1897    Intorno  alia  ghiandola  pineale  dei  mammiferi.    Moni- 

tore  Zoologico  ItaL,  T.  8,  No.  1. 

373  STANNIUS     1854    Lehrbuch  d.  vergleichende  Anat.  der  Wirbeltiere,  S.  59. 

374  STEMMLER,    J.     1900    Die   Entwicklung   der  Anhange   am   Zwischenhirn- 

dach  beim  Gecko  (Gehyra  oceanica  und  Hemidactylus  mabouia). 
Ein  Beitrag  zur  Kenntnis  der  Epiphysis,  des  Parietalorganes  und 
der  Paraphyse.  Leipziger  Dissertation.  Limburg. 

375  STIEDA,  L.     1865    t)ber  den  Bau  der  Haut  des  Frosches  (Rana  temporaria). 

Archiv.  f.  Anat,  Phys.  u.  wiss.  Med.,  S.  52. 

376  1869    Studien  iiber  das  zentrale  Nervensystem  der  Vogel  und  Sauge- 
tiere.     Zeitschr.  f.  wiss.  ZooL,  Bd.  19. 

377  1870    Studien  uber  das  zentrale  Nervensystem  der  Wirbeltiere  (Frosch, 
Kaninchen,  Hund).     Zeitschr.  f.  wiss.  ZooL,  Bd.  20. 

378  1873    tiber  die  Deutung  der  einzelnen  Teile  des  Fischgehirns.     Zeit- 
schr. f.  wiss.  ZooL,  Bd.  23. 

379  1875    Uber  den  Bau  des  zentralen  Nervensystems  der  Amphibien 
und  Reptilien. 

380  1875    tiber  den  Bau  des  zentralen  Nervensystems  des  Axolotl. 

381  •       1875    tiber  den  Bau  des  zentralen  Nervensystems  der  Schildkrote. 

Zeitschr.  f.  wiss.  ZooL,  Bd.  25. 

382  STRAHL,    IL     1884    Das  Leydigsche   organ  bei   Eidechsen.     Sitzungsber. 

d.  Gesellschaf t  zur  Beforderung  d.  ges.  Naturwissenschaf ten  zu  Mar- 
burg, Mai. 

383  STRAHL,  H.  AND  MARTIN,  E.     1888    Die  Entwicklungsgeschichte  des  Parie- 

t#lauges  bei  Anguis  fragilis  and  Lacerta  vivipara.  Arch.  f.  Anat. 
und  Phys.,  Anat.  Abt.,  S.  146-161. 


256  FREDERICK    TILNEY    AND    LUTHER    F.    WARREN 

384  STUDNICKA,  F.  K.     1893     Sur  les  organes  parietaux  de  Petromyzon  planeri. 

Sitzungsber.  der.  Kg.  Ges.  d.  Wissensch.  in  Prag. 

385  1895    Zur  Anatomie  der  sogenanntenParaphyse  des  Wirbeltiergehirns. 
Sitzungsber.  der  Kg.  Ges.  d.  Wissensch.  in  Prag. 

386  1895-6    Beitrage    zur    Anatomie    und    Entwicklungsgeschichte    des 
Vorderhirns  der  Kranioten.     Idem.,  Abt.  1,  1895,  2,  1896. 

387  1898    Zur  Kritik  einiger  Angaben  uber  die  Existenz  eines  Parietal- 
auges  bei  Myxine  glutinosa.     Idem.     , 

388  1899    tJber  den   feineren   Bau   der  Parietalorgane   von   Petromyzon 
marinus.     Idem. 

389  1900    Zur  Kenntnis  der  Parietalorgane  und  der  sog.  Paraphyse  der 
niederen  Wirbeltiere.     Verhandl.  der  Anat.  Ges.  auf  der  XVII  Ver- 
sammlung  in  Pavia. 

390  1900     Untersuchungen  iiber  das  Ependym  der  nervosen  Zentralorgane. 
Anatom.  Hefte,  Bd.  15. 

391  1905    Die  Parietalorgan.     In  Oppel-Lehrb.  d.  vergl.  mikrosk,  Anat. 
d.  Wirbelt.,  Bd.  5  (Monograph). 

392  TERRY,  R.  J.     1911     The  morphology  of  the  pineal  region  in  Teleosts. 

Jour.  Morph.,  vol..  21,  p.  321. 

393  TESTUT    1900    Traite  d'Anat,  Humaine.  4  ed.,  T.  2. 

394  TIEDEMANN,    F.     1816    Anatomie    und    Bildungsgeschichte    des    Gehirns 

im  Fotus  des  Menschen.     Niirnberg,  S.  172. 

395  1823    Anatomie  du  Cerveau.     Trad,  par  a  Jourdan.     Paris. 

396  TILNEY,  F.     1915    The  morphology  of  the  diencephalic  floor.     Jour.  Comp. 

Neur.,  vol.  25,  p.  213. 

397  TOLDT    1888    Lehrbuch  der  Gewebelehre. 

398  TOURNEUX     1909     Embryologie  humaine.     Paris. 

399  TURNER,    C.    H.     1891     Morphology   of   the    avian    brain.     Jour.    Comp. 

Neur.,  vol.  1. 

400  TURNER,  W.     1888    The  pineal  body  (Epiphysis  cerebri)  in  the  brain  of 

the  walrus  and  seals.     Jour,  of  Anat.  and  Physiol.,  vol.  22.     (Referat 
in  Hermann  Schwalbes  Jahresb.,  Bd.  17,  p.  261.) 

401  UVARTHONUS     Cited  by  Cuto re  in :  II  Corpo  Pineale  di  Alcuni  Mammiferi. 

Arch.  Ital.  di  Anat.  e.  di  Embriol.  1910-11,  T.  9,  p.  403. 

402  Ussow     1882    De  la  structure  des  lobes  accessoires  de  la  moelle  epiniere 

de  quelques  poissons  osseux.     Archiv.  de  Biol.,  T.  3. 

403  VALENTIN    1843    Trait£   de   Neurologic.     Trans,    by  A.    J.    L.    Jourdan, 

Paris,  p.  164. 

404  VAN    GEHUGHTEN    1906    Anatomie    du    systeme    nerveux    de    PHomme. 

Louvain. 

405  VARIGNI,  H.     1886    Le  troisieme  oeil  des  Vertcbres.     Revue  scientifique. 

406  VAN  WIJHE,  J.  W.     1883    Uber  die  Mesodermsegmente  und  die  Entwick- 

lungsgeschichte  der   Nerven   des  Selachierkopfes.    Verhandl.    d.    k. 
Akad.  d.  Wetensch.,  Bd.  22.     Amsterdam. 

407  1884    Uber  den  vorderen  Neuroporus  und  die  phylogenetische  Funk- 
tion  des  Canalis  neurentericus  der  Wirbeltiere.     Zoolog.  Anzeiger,  7. 

408  VICQ-D'AZYE     1781     Memoires  de  1'Acad.  roy  des  Sciences. 

409  VIRCHOW     Cited  by  Legros,  These  de  Paris,  1873. 


THE    PINEAL   BODY  257 

410  VOELTZKOW,    A.     1903    Epiphyse    und    Paraphyse    bei    Krokodilen    und 

Schildkroten.     Abhandl.  d.  Senckenberg.  Naturf.  Ges.,  Bd.  27. 

411  VOLTAIRE     Cited  by  Majendie  in:  Memoir  physiologique  experimentale 

et  pathologique.     T.  7,  p.  211,  1828. 

412  WALDSCHMIDT,  J.     1887    Beitrag  zur  Anatomie  des  Zentralnervensystems 

und  des  Geruchsorganes  von  Polypterus  bichir.     Anat.  Anz.,  2. 

413  1887    Zur  Anatomie  des  Nervensystems  der  Gymnophionen.     Zeit. 
f.  Med.  u.  Naturwiss,  Bd.  20. 

414  WALTER,  F.  K.     1913    Beitragezur  histologiedermenschlichen  Zirbeldrtise. 

Zeit.  p.  d.  ges.  Neurol.  in  Psychiat.  Bd.  27,  S.  65. 

415  WARREN,  J.     1911     The  development  of  tlie  paraphysis  and  pineal  region 

in  Reptilia.     Amer.  Jour.  Anat.,  vol.  2,  p.  313. 

416  1906    The  development  of  the  paraphysis  and  pineal  region  in  Nec- 
turus  maculata.     Amer.  Jour.  Anat.,  p.  1. 

417  1917    The  development  of  the  paraphysis  and  pineal  region  in  Mam- 
malia.    Jour.  Comp.  Neur.,  vol.  28. 

418  WEIGERT,  C.     1875    Virchow's  Arch.  f.  path.  Anat.,  65,  p.  212. 

419  1895    Beitrag  zur  Kenntnis  normalen  menschlichen  Neuroglia.  Ab- 
handl. d.  Senckenbg.  Naturf.  ges.  Frankfurt  a/M.,  Bd.  19. 

420  WENZEL,  J.  A.     1812    De  penitiori  structura  cerebri  hominis  atque  bru- 

torum.     Tiigingae. 

421  WHITWELL,  J.  R.     1888    The  epiphysis  cerebri  in  Petromyzon  fluviatilis. 

Jour,  of  Anat.  and  Physiol. 

422  WIEDERSHEIM,  R.     1880    Das  Gehirn  von  Ammocoetes  und  Petromyzon 

planeri  mit  besonderer  Beriicksichtigung    der    spinalartigen    Hirn- 
nerven.     Jena.  Zeit.,  Bd.  14,  S.  7. 

423  1880    Skelet  und  .Nervensystem  von  Lepidosiren  annectens.    Jena. 
Zeit,,  Bd.  14. 

424  1886    tiber  das  Parietalauge  der  Saurier.     Anat.  Anz.,  1. 

425  1898    Grundriss  der  vergleichenden  Anatomie  der  Wirbeltiere.     Jena. 

426  WILDER,  B.  G.     1896    The  names  epiphysis,  conarium  and  corpus  pineale. 

Correction  of  an  error.     Science,  N.  S.,  vol.  4,  no.  85. 

427  1887    The  Dipnoian  brain.     Amer.  Naturalist,  June. 

428  1896    The  dorsal  sac,  the  aulix  and  the  diencephalic  flexure.     Jour. 
Comp.  Neur.,  vol.  6. 

429  WILLIS,  T.     Cerebri  anatome.     Cap.  14,  p.  46. 

430  WRIGHT,  RAMSAY    1884    On  tjhe  nervous  system  and  sense  organs  of  Ami- 

urus.     Proceed.  Canad.  Insfy  Toronto,  vol.  2,  Fasc.  3. 

431  WYMAN    1853    Anatomy  of  the  nervous  system  of  Rana  pipiens.     Smith- 

sonian Contributions  to  Knowledge,  vol.  4. 

432  ZANCLA    1906    Sulla  fine  struttura  del  Conarium  umano.     Arch,  di  Anat. 

patolog.  e  Scienze  -afnni,  2,  Palermo. 


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